Tone reproduction characteristics measuring device for color monitor

ABSTRACT

The tone reproduction characteristics of a color monitor are determined at high precision by visual recognition. A pattern display means ( 230 ) displays a test pattern, comprising circular patterns ( 50 ) and a background ( 60 ), on the screen of the monitor ( 100 ) to be measured. In the background ( 60 ), a reference pattern, which is generated by a reference pattern generating means ( 220 ), is formed of a black-and-white pattern, and has a prescribed reference luminance, is displayed, and in each circular pattern ( 50 ), an even pattern with RGB tone values designated by a tone value designating means ( 210 ) is displayed. The tone of the even pattern is varied so as to vary in brightness and color by a tone value varying means ( 240 ). When the circular patterns ( 50 ) become the same in brightness and color as the background ( 60 ), an operator provides a coincidence signal to a coincidence signal input means ( 250 ). A characteristics computing means ( 260 ) computes curves, indicating the tone reproduction characteristics according to the respective colors of R, G, and B, based on the reference luminance and the corresponding tone values at this point. The circular patterns ( 50 ) are positioned at a pitch that is in accordance with the spatial frequency sensitivity of human eyes.

TECHNICAL FIELD

This invention relates to a tone reproduction characteristics measuringdevice for color monitor, and particularly relates to a device fordetermining, by visual recognition, tone reproduction characteristics,which indicate the relationship between input signal tone values andactual display luminance, of a color monitor having a function ofdisplaying color images using the three primary colors, R, G, and B.

BACKGROUND ART

Generally, the display characteristics of monitors (display devices)differ according to each individual product, and in the case of use uponconnection to a personal computer, etc., corrections are preferablycarried out in accordance with the individual display characteristics.To carry out such corrections, the display characteristics of eachindividual monitor must be measured and the results must be prepared asobjective data in advance. Normally, such data are referred to as theprofile data of each individual monitor. In connecting a monitor to apersonal computer, by incorporating the profile data of the monitor inthe personal computer, corrections based on the profile data are enabledand universal display results that are not affected by the displaycharacteristics unique to the individual monitor can be obtained.

The representative display characteristics of a color monitor having afunction of displaying color images using the three primary colors, R,G, and B, are the chromaticities of the three primary colors, thechromaticity of white, and the tone reproduction characteristics. Here,the tone reproduction characteristics indicate the relationship betweeninput signal tone values and actual display luminance and is normallycalled the gamma characteristics. If corrections that are in accordancewith the tone reproduction characteristics are not carried out,individual monitors will perform image displays that differ in luminousdistribution even if the displayed image is based on exactly the sameimage data. The performing of corrections in accordance with the uniquetone reproduction characteristics of each individual monitor (so-calledgamma correction) is thus extremely important for practical use. Ageneral method for such gamma correction is disclosed for example inJapanese Unexamined Patent Publication No. 162714/1995.

Though among methods of measuring the tone reproduction characteristicsof each individual monitor, there are methods wherein physicalcharacteristics data are obtained using an optical measuring device, amethod of obtaining characteristics data while carrying out visualrecognition by human eyes is normally employed. This is because amonitor is actually used by humans and characteristics data obtained bya measurement method based on luminance perceived sensually by humanvision are preferable over characteristics data obtained by a purelyphysical measurement method. A method of obtaining tone reproductioncharacteristics by visual recognition is, for example, disclosed inJapanese Patent Publication No. 2889078.

Though as mentioned above, the obtaining of tone reproductioncharacteristics by visual recognition for each individual monitor isextremely important in terms of performing corrections that match thesensitivity characteristics of human eyes, tone reproductioncharacteristics cannot be determined at adequate precision withconventionally proposed measuring methods and measuring devices usingvisual recognition. In particular, in the case of a color monitor usedin DTP processes for preparing printed matter, tone reproductioncharacteristics must be determined at higher precision in order toperform corrections of high precision. However, with conventional arts,measurements of adequate precision cannot be carried out on liquidcrystal color displays or CRT color monitors that have undergone ageddeterioration.

An object of this invention is thus to provide a tone reproductioncharacteristics measuring device for color monitor that enables the tonereproduction characteristics to be determined at high precision byvisual recognition.

DISCLOSURE OF INVENTION

(1) The first feature of the present invention resides in a device formeasuring tone reproduction characteristics, which indicate arelationship between input signal tone values and actual displayluminance of a color monitor having a function of displaying colorimages using three primary colors of R, G, and B, the tone reproductioncharacteristics measuring device for color monitor comprising:

tone value designating means, designating a combination of tone valuesof the three primary colors, R, G, and B, for displaying an even patternof uniform brightness and color in a first attribute region;

reference pattern generating means generating a reference pattern inwhich first sub-regions and second sub-regions are mixed at a prescribedarea ratio inside a second attribute region, wherein each of the threeprimary colors, R, G, and B take on a minimum tone value in the firstsub-regions and each of the three primary colors, R, G, and B take on amaximum tone value in the second sub-regions;

pattern display means defining a test pattern which is arranged from thefirst attribute region and the second attribute region being positionedso as to contact each other on a screen of the color monitor, andproviding prescribed signals to the color monitor so that an evenpattern, based on the combination of tone values designated by the tonevalue designating means, is displayed in the first attribute region, andthe reference pattern, generated by the reference pattern generatingmeans, is displayed in the second attribute region;

tone value varying means varying respective tone values designated bythe tone value designating means so as to vary a brightness and a colorof the even pattern;

coincidence signal input means inputting, while a varying operation bythe tone value varying means is being performed, a coincidence signalindicating a recognition that the first attribute region and the secondattribute region are matched in both brightness and color, from anoperator who views the test pattern displayed on the screen of the colormonitor; and

characteristics computing means recognizing a combination of tone valuesdesignated by the tone value designating means at a point when thecoincidence signal is input, as corresponding tone values of therespective primary colors that correspond to a prescribed referenceluminance in accordance with the prescribed area ratio, and determining,by computation, tone reproduction characteristics of the respectiveprimary colors based on the reference luminance and the correspondingtone values that correspond to each other.

(2) The second feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first feature, wherein:

the tone value varying means has a function of performing two types ofvarying operations of a brightness varying operation, with which thetone values are varied so that mainly a brightness of the even patternchanges, and a color varying operation, with which a tone value isvaried so that mainly a color of the even pattern changes.

(3) The third feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the second feature, wherein:

the brightness varying operation is performed by a task of increasing ordecreasing all of respective tone values of the three primary colors, R,G, and B by a common variation amount, and

the color varying operation is performed by a task of increasing ordecreasing a tone value of a single specific color among the threeprimary colors, R, G, and B.

(4) The fourth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first to third features, wherein:

the tone value varying means performs variations of the tone valuesbased on operation inputs by the operator.

(5) The fifth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the fourth feature, wherein:

the tone value varying means uses a first button that provides aninstruction of making the even pattern brighter, a second button thatprovides an instruction of making the even pattern darker, a thirdbutton that provides an instruction of strengthening a component of aspecific color of the even pattern, and a fourth button that provides aninstruction of weakening a component of the specific color of the evenpattern, and performs a varying operation of adding a common variationamount to all of the respective tone values of the three primary colors,R, G, and B, when there is an operation input in regard to the firstbutton, performs a varying operation of subtracting a common variationamount from all of the respective tone values of the three primarycolors, R, G, and B, when there is an operation input in regard to thesecond button, performs a varying operation of adding a prescribedvariation amount to a tone value of the specific color when there is anoperation input in regard to the third button, and performs a varyingoperation of subtracting a prescribed variation amount from a tone valueof the specific color when there is an operation input in regard to thefourth button.

(6) The sixth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the fifth feature, wherein:

a two-dimensional XY coordinate system is defined and the respectivebuttons are positioned so that the first button and the second buttonare positioned at opposing positions along an X-axis that sandwich anorigin and the third button and the fourth button are positioned atopposing position along a Y-axis that sandwich the origin.

(7) The seventh feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first to third features, wherein:

the tone value varying means varies the tone values with time inaccordance with prescribed rules that have been established in advance.

(8) The eighth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the seventh feature, wherein:

the tone value varying means has a function of performing two varyingoperations of a brightness varying operation, wherein, by adding orsubtracting a common variation amount at a prescribed timing to or fromall of respective tone values of the three primary colors, R, G, and B,the tone values are varied so that mainly the brightness of the evenpattern changes, and a color varying operation, wherein, by adding orsubtracting a prescribed variation amount at a prescribed timing to orfrom a tone value of one specific color among the three primary colors,R, G, and B, the tone value is varied so that mainly the color of theeven pattern changes, and

-   -   the coincidence signal input means has a brightness coincidence        signal input means, for inputting, while the tone value varying        means is performing the brightness varying operation, a        brightness coincidence signal that indicates a recognition that        the brightness is matched from the operator, and a color        coincidence signal input means, for inputting, while the tone        value varying means is performing the color varying operation, a        color coincidence signal that indicates a recognition that the        color is matched from the operator, and deems that a coincidence        signal indicating a recognition of matching of both brightness        and color is input when both inputs of the brightness        coincidence signal and the color coincidence signal are        completed.

(9) The ninth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the eighth feature, wherein:

when a tone value obtained by a varying operation of adding a variationamount exceeds a maximum tone value, a circulation process ofincrementing a minimum tone value by an excess amount is performed, andwhen a tone value obtained by a varying operation of subtracting avariation amount falls below the minimum tone value, a circulationprocess of decrementing a maximum tone value by an excess amount isperformed.

(10) The tenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the eighth or ninth feature, wherein:

the tone value varying means has a function of starting the colorvarying operation at a point when the brightness coincidence signal isinput while the brightness varying operation is performed, starting thebrightness varying operation at a point when the color coincidencesignal is input while the color varying operation is performed, andrepeatedly executing the brightness varying operation and the colorvarying operation in alternation and has a function of performing arepeated execution while gradually decreasing the tone value variationamount, and

the coincidence signal input means deems that the coincidence signalindicating a recognition of matching of both brightness and color isinput when both inputs of the brightness coincidence signal and thecolor coincidence signal are completed after the variation amount hasreached a predefined value.

(11) The eleventh feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the third, fifth or eighth feature, wherein:

of the three primary colors, R, G, and B, the primary color B is deemedto be the specific color and tone reproduction characteristics for theprimary color B and tone reproduction characteristics in common to theprimary colors R and G are determined.

(12) The twelfth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first to eleventh features, wherein:

the reference pattern generating means has a function of setting aplurality N of area ratios of the first sub-regions to the secondsub-regions and generating N reference patterns that differ mutually inreference luminance, and

the characteristics computing means has a function of determining thetone reproduction characteristics for the respective primary colorsbased on N corresponding tone values obtained for N test patterns usingthe N reference patterns.

(13) The thirteenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the twelfth feature, wherein:

the characteristics computing means defines a two-dimensional coordinatesystem in which a first coordinate axis is set for tone value and asecond coordinate axis is set for luminance, plots N points havingrespective luminance values and corresponding tone values as coordinatevalues on the coordinate system, plots a point having a minimumluminance value and a minimum tone value as coordinate values, and apoint having a maximum luminance value and a maximum tone value ascoordinate values, and determines a curve passing through the total of(N+2) plotted points in a form of a graph that indicates the tonereproduction characteristics.

(14) The fourteenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the thirteenth feature, wherein:

N is set equal to 3, a total of five points are plotted, and uponreferring to these five points as a first point to a fifth point in theorder of increasing coordinate value along the first coordinate axis, afirst function curve, passing through the first, second, and thirdpoints and taking a form of expressing the luminance as a power of thetone value, and a second function curve, passing through the third,fourth, and fifth points and taking a form of expressing the luminanceas a power of the tone value are determined by computation, and a curveformed by joining the first function curve and the second function curveis deemed to be the curve expressing the tone reproductioncharacteristics.

(15) The fifteenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first to fourteenth features, wherein:

the reference pattern generating means forms the first sub-regions andthe second sub-regions from unit cells having the same shape and sizeand forms the reference pattern from a two-dimensional array of theseunit cells.

(16) The sixteenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the fifteenth feature, wherein:

the reference pattern is formed by arraying rectangular unit cells in atwo-dimensional array, and for arbitrary odd numbers i and j, a cellgroup, formed of four unit cells of a unit cell of an i-th row and aj-th column, a unit cell of the i-th row and a (j+1)-th column, a unitcell of an (i+1)-th row and the j-th column, and a unit cell of the(i+1)-th row and the (j+1)-th column, is defined, and a commonpositioning pattern of the first sub-regions and the second sub-regionsis applied for all cell groups.

(17) The seventeenth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the sixteenth feature, wherein:

among the four unit cells which make up a cell group, first sub-regionsare formed by a pair of unit cells adjacent diagonally and secondsub-regions are formed by a remaining pair of unit cells so as toconstitute a reference pattern with an area ratio of 1:1.

(18) The eighteenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the sixteenth feature, wherein:

among the four unit cells which make up a cell group, one unit cellconstitutes one sub-region and remaining three unit cells constitute theother sub-region so as to constitute a reference pattern with an arearatio of 3:1 or 1:3.

(19) The nineteenth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first to eighteenth features, wherein:

a contour of the first attribute region or the second attribute regionthat makes up the test pattern is made of a circle or an ellipse.

(20) The twentieth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the first to nineteenth features, wherein:

one attribute region that makes up the test pattern is made of aplurality of regions positioned in a dispersed manner and the otherattribute region is made of a background portion thereof.

(21) The twenty-first feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twentieth feature, wherein:

a total area of the first attribute region is made equal to a total areaof the second attribute region.

(22) The twenty-second feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twentieth or twenty-first feature, wherein:

a plurality of regions of the same attribute that are the same in shapeand size are positioned dispersedly in a two-dimensional plane at aprescribed pitch so that a prescribed spatial frequency is obtained.

(23) The twenty-third feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-second feature, wherein:

a plurality of one-dimensional region arrays, in each of which aplurality of regions of the same attribute are positioned in ahorizontal direction at a prescribed pitch Px, are positioned in avertical direction at a prescribed pitch Py (where Py=(√{square rootover ( )}3)/2·Px) and positioned so that among mutually adjacentone-dimensional region arrays, the phase is shifted by half a pitch.

(24) The twenty-fourth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-second or twenty-third feature, wherein:

regions of the same attribute are positioned dispersedly at a prescribedpitch by which a spatial frequency that exhibits good sensitivity inregard to both brightness difference discrimination characteristics andcolor difference discrimination characteristics for the operator viewingthe test pattern is obtained.

(25) The twenty-fifth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-second or twenty-third feature, wherein:

a first pitch, by which a spatial frequency that exhibits goodsensitivity in regard to brightness difference discriminationcharacteristics for the operator viewing the test pattern is obtained,and a second pitch, by which a spatial frequency that exhibits goodsensitivity in regard to color difference discrimination characteristicsfor the operator viewing the test pattern is obtained, are set, and

the pattern display means has a function of displaying a test pattern,formed by dispersedly positioning regions of the same attribute at thefirst pitch, when a brightness matching recognition task is performed bythe operator, and displaying a test pattern, formed by dispersedlypositioning regions of the same attribute at the second pitch, when acolor matching recognition task is performed by the operator.

(26) The twenty-sixth feature of the present invention resides in aprogram for making a computer function as the measuring device accordingto the first to twenty-fifth features, or a computer-readable recordingmedium in which the program is recorded.

(27) The twenty-seventh feature of the present invention resides in adevice for measuring tone reproduction characteristics, which indicate arelationship between input signal tone values and actual displayluminance of a color monitor having a function of displaying colorimages using three primary colors of R, G, and B, the tone reproductioncharacteristics measuring device for color monitor comprising:

tone reproduction characteristics storage means storing provisional tonereproduction characteristics;

image data storage means storing image data of a sample image to be usedin measurement;

image display means which assumes that the tone reproductioncharacteristics of the color monitor are to be the provisional tonereproduction characteristics stored in the tone reproductioncharacteristics storage means, performs prescribed tone corrections onimage data stored in the image data storage means so that the sampleimage will be displayed with correct tone reproduction on the colormonitor, and provides corrected image data to the color monitor;

a physical output medium obtained by outputting the sample image on aphysical medium based on the image data stored in the image data storagemeans;

characteristics modifying means receiving instruction inputs, for makinga sample image displayed on a screen of the color monitor, and a sampleimage displayed on the physical output medium, close in brightness andcolor, from an operator who visually compares the two images;

coincidence signal input means inputting a coincidence signal,indicating a recognition that both of the images are matched both inbrightness and color, from the operator; and

characteristics output means outputting the provisional tonereproduction characteristics, stored in the tone reproductioncharacteristics storage means when the coincidence signal is input, as aformal tone reproduction characteristics of the color monitor.

(28) The twenty-eighth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-seventh feature, wherein:

image data of a plurality M of sample images that differ in overallbrightness are stored in the image data storage means and M physicaloutput media, respectively corresponding to the M sample images, areprepared; and

the characteristics modifying means, upon receiving an instruction inputconcerning an i-th sample image among the M sample images, performsmodifications stressed on “a portion corresponding to a brightness ofthe i-th sample image” on the provisional tone reproductioncharacteristics stored in the tone reproduction characteristics storagemeans.

(29) The twenty-nineth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-eighth feature, wherein:

the tone reproduction characteristics storage means stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and

the characteristics modifying means, upon receiving an instruction inputconcerning an i-th sample image, recognizes a point on a curve, having arepresentative tone value of the i-th sample image, as a control point,and after moving the control point in a prescribed direction inaccordance with the instruction input, modifies the curve smoothly sothat it passes through the control point after movement.

(30) The thirtieth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the twenty-ninth feature, wherein:

a mode value or an average value of pixel values of all colors ofindividual pixels indicated by the image data stored in the image datastorage means is used as a representative tone value of the sampleimage.

(31) The thirty-first feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-eighth feature, wherein:

the tone reproduction characteristics storage means stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and

the characteristics modifying means, upon receiving an instruction inputconcerning an i-th sample image, recognizes a point on a curve, having arepresentative luminance value of the i-th sample image, as a controlpoint, and after moving the control point in a prescribed direction inaccordance with the instruction input, modifies the curve smoothly sothat it passes through the control point after movement.

(32) The thirty-second feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-first feature, wherein:

a mode value or an average value of pixel values of all colors ofindividual pixels indicated by the image data stored in the image datastorage means is determined as the representative tone value of thesample image, and a value converted by a prescribed conversion methodbased on the determined representative tone value is used as therepresentative luminance value of the sample image.

(33) The thirty-third feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-first feature, wherein:

an actually measured value of luminance of an entire sample image on thephysical output medium is used as the representative luminance value ofthe sample image.

(34) The thirty-fourth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-seventh feature, wherein:

the characteristics modifying means performs processes of varying thetone reproduction characteristics with time in accordance withprescribed rules that have been established in advance and performsmodifications wherein provisional tone reproduction characteristics whenan instruction input from the operator is provided are deemed to be newprovisional tone reproduction characteristics.

(35) The thirty-fifth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-fourth feature, wherein:

image data of a plurality M of sample images that differ in overallbrightness are stored in the image data storage means and M physicaloutput media, respectively corresponding to the M sample images areprepared; and

the characteristics modifying means has a function of executingprocesses of performing variations stressed on “a portion correspondingto a brightness of an i-th sample image among the M sample images” onthe provisional tone reproduction characteristics stored in the tonereproduction characteristics storage means for each of i=1 to M.

(36) The thirty-sixth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-fifth feature, wherein:

the tone reproduction characteristics storage means stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and

the characteristics modifying means, in executing a process ofperforming variations stressed on “a portion corresponding to abrightness of an i-th sample image,” recognizes a point on each of thecurves, having a representative tone value of the i-th sample image, asa control point, moves the control point in prescribed directionscyclically, and modifies the curve smoothly so that it passes throughthe control point after movement.

(37) The thirty-seventh feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-sixth feature, wherein:

a mode value or an average value of pixel values of all colors ofindividual pixels indicated by the image data stored in the image datastorage means is used as the representative tone value of the sampleimage.

(38) The thirty-eighth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-fifth feature, wherein:

the tone reproduction characteristics storage means stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and

the characteristics modifying means, in executing a process ofperforming variations stressed on “a portion corresponding to abrightness of an i-th sample image,” recognizes a point on each of thecurves, having a representative luminance value of the i-th sampleimage, as a control point, moves the control point in prescribeddirections cyclically, and modifies the curve smoothly so that it passesthrough the control point after movement.

(39) The thirty-ninth feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the thirty-eighth feature, wherein:

a mode value or an average value of pixel values of all colors ofindividual pixels indicated by the image data stored in the image datastorage means is determined as the representative tone value of thesample image, and a value converted by a prescribed conversion methodbased on the determined representative tone value is used as therepresentative luminance value of the sample image.

(40) The fortieth feature of the present invention resides in the tonereproduction characteristics measuring device for color monitoraccording to the thirty-eighth feature, wherein:

an actually measured value of luminance of an entire sample image on thephysical output medium is used as the representative luminance value ofthe sample image.

(41) The forty-first feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-seventh to fortieth features, wherein:

the characteristics modifying means has a function of performing twotypes of modifying operations of a brightness modifying operation ofmodifying the tone reproduction characteristics based on an instructioninput for mainly changing the brightness of the sample image displayedon a screen of the color monitor, and a color modifying operation ofmodifying the tone reproduction characteristics based on an instructioninput for mainly changing the color.

(42) The forty-second feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to forty-first feature, wherein:

the tone reproduction characteristics storage means stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and

the characteristics modifying means, performs modification on all of therespective curves of the three primary colors R, G, and B in performingthe brightness modifying operation, and performs modification on only acurve of a color to be modified in performing the color modifyingoperation.

(43) The forty-third feature of the present invention resides in thetone reproduction characteristics measuring device for color monitoraccording to the twenty-seventh to forty-second features, wherein:

an image, which can be recognized as a substantially achromatic imagewhen viewed by the operator, is used as the sample image.

(44) The forty-fourth feature of the present invention resides in aprogram for making a computer function as the tone reproductioncharacteristics storage means, image data storage means, image displaymeans, characteristics varying means, coincidence signal input means,and characteristics output means in the measuring device according tothe twenty-seventh to forty-third features or a computer-readablerecording medium in which the program is recorded.

(45) The forty-fifth feature of the present invention resides in adevice for measuring tone reproduction characteristics, which indicate arelationship between input signal tone values and actual displayluminance of a color monitor having a function of displaying colorimages using three primary colors of R, G, and B, the tone reproductioncharacteristics measuring device for color monitor comprising:

means for determining a correspondence between luminance and tone valueby visual recognition;

means for determining a combination of tone values of the three primarycolors that appears to be achromatic; and

characteristics computing means determining, by computation, the tonereproduction characteristics for the respective primary colors from thecorrespondence between luminance and tone value and a combination of thethree primary colors.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a state wherein a personal computer200, which is to function as a monitor characteristics measuring device,is connected to a monitor 100, which is to be measured.

FIG. 2 is a graph showing the general tone reproduction characteristicsof a monitor.

FIGS. 3A and 3B are diagrams illustrating the basic principles of arepresentative method for measuring tone reproduction characteristics byvisual recognition, with FIG. 3A being a plan view showing a testpattern to be displayed to an operator and FIG. 3B being a partiallyenlarged view of a second attribute region 20 inside the test pattern.

FIG. 4 is a graph showing the tone reproduction characteristicsdetermined based on the measurement results using the test pattern shownin FIGS. 3A and 3B.

FIG. 5 is a graph showing the results of measuring tone reproductioncharacteristics for each of the primary colors for a general colormonitor.

FIG. 6 is a plan view showing an example of an operation panel used forcarrying out a brightness varying operation and a color varyingoperation based on operation inputs of an operator.

FIG. 7 is a plan view showing another example of an operation panel usedfor carrying out a brightness varying operation and a color varyingoperation based on operation inputs of an operator.

FIG. 8 is a plan view showing an example of an operation panel used forcarrying out a brightness varying operation and a color varyingoperation automatically and making an operator perform a matching inputoperation.

FIG. 9 is a flowchart showing an example of a processing procedure ofrepeatedly executing an operation of matching the brightness and anoperation of matching the color in alternation.

FIG. 10 is a graph for describing an embodiment for determining anapproximate function curve that passes through the five points O, Q1,Q2, Q3, and P by computation.

FIG. 11 is a graph for describing the computation in a case where theapproximate function curve that passes through the five points O, Q1,Q2, Q3, and P is a sigmoid curve.

FIG. 12A is plan view showing a new test pattern by which morepreferable measurement results can be obtained, and FIG. 12B is anenlarged view of a reference pattern that is displayed inside secondattribute region 60 of this test pattern.

FIG. 13A is a plan view showing an example wherein a reference patternof a reference luminance of 25% is formed using a reference pattern,wherein rectangular unit cells are arrayed in a two-dimensional array,and FIG. 13B is a plan view showing an example wherein a referencepattern of a reference luminance of 75% is formed using a referencepattern, wherein rectangular unit cells are arrayed in a two-dimensionalarray.

FIG. 14 is a plan view of an example wherein regions 70 of the sameattribute are formed by circles of the same radius r and positioned at aprescribed pitch on a two-dimensional plane.

FIG. 15 is a plan view for describing the sensitivity of a visualperception system wherein a pair of objects (circular regions of thesame attribute) 70 are positioned at a pitch Px.

FIG. 16 is a graph showing the sensitivity characteristics of the humanvisual perception system, with the abscissa indicating the spatialfrequency of an observed object (unit: cycle/deg) in logarithmic scaleand the ordinate indicating the relative sensitivity value of the humanvisual perception system for distinguishing brightness differences andcolor differences of an object.

FIG. 17 is a table showing the respective optimal values extracted fromthe graph shown in FIG. 16.

FIG. 18 is a block diagram showing the basic arrangement of thisinvention's tone reproduction characteristics measuring device for colormonitor.

FIG. 19 is a plan view showing sample images used in another tonereproduction characteristics measuring method for color monitor by thisinvention.

FIG. 20 is a graph showing the principles of tone reproductioncharacteristics modification in the tone reproduction characteristicsmeasuring method using the sample images shown in FIG. 19.

FIG. 21 is a plan view showing an example of a screen for modificationoperation by an operator using sample image Ha shown in FIG. 19.

FIG. 22 is a plan view showing an example of a screen for modificationoperation by an operator using sample image Hb shown in FIG. 19.

FIG. 23 is a plan view showing an example of a screen for modificationoperation by an operator using sample image Hc shown in FIG. 19.

FIG. 24 is a block diagram showing the basic arrangement of areproduction characteristics measuring device for color monitor thatuses a sample image by this invention.

FIG. 25 is a flowchart illustrating the characteristics measurementprocess procedures using the measuring device shown in FIG. 24.

FIG. 26 is a diagram showing the representative tone values and therepresentative luminance values determined for the respective sampleimages shown in FIG. 19.

FIG. 27 is a graph showing the principles of tone reproductioncharacteristics modification in the tone reproduction characteristicsmeasuring method using the sample images shown in FIG. 26.

BEST MODE FOR CARRYING OUT THE INVENTION

This invention will now be described based on the illustratedembodiments.

<<<Section 1. General Conventional Method for Measuring ToneReproduction Characteristics by Visual Recognition>>>

First, the basic principles of a generally-practiced, conventionalmethod for measuring tone reproduction characteristics by visualrecognition will be described. As shown in the block diagram of FIG. 1,in order to measure monitor characteristics by visual recognition, apersonal computer 200, which is connected to a monitor 100 that is to bemeasured, can be normally used as a monitor characteristics measuringdevice. That is, by installing a program for measuring tone reproductioncharacteristics in personal computer 200 in advance and by making thisprogram operate to make test patterns, to be described later, bedisplayed on the screen of monitor 100 and obtaining responses from anoperator using an input equipment of personal computer 200, the datanecessary for measurement can be taken in.

Though a method for measuring tone reproduction characteristics(so-called gamma characteristics), which is directly relevant to thepresent invention, will be described here, by using personal computer200 that functions as a monitor characteristics measuring device, thechromaticities of the three primary colors, the chromaticity of white,and other characteristics can also be measured, and such measurementresults are generally referred to as monitor profile data based onvisual recognition. Monitor 100, which is to be the object ofmeasurement of the profile data, is not limited to a CRT monitor and mayalso be a liquid crystal display, etc. In the present Specification, theterm “monitor” is the same in definition as “display device” and widelyrefers to devices having a function of displaying an image based onelectrical signals. Also, normally in connecting monitor 100 to personalcomputer 200, a graphics board, which serves as an interface fortransferring image signals, is used, and since such a graphics board andother image processing circuits are components that affect the displaycharacteristics of monitor 100, these components make up a portion ofthe object of measurement by the monitor characteristics measuringdevice. In other words, with the present invention, “monitor 100” is aconcept that includes an image processing circuit, such as a graphicsboard.

FIG. 2 is a graph showing general tone reproduction characteristics of amonitor. As is illustrated, this tone reproduction characteristics graphindicates the relationship between the tone value of an input signalprovided to monitor 100 and the actual display luminance obtained on thescreen of monitor 100. Here, for the convenience of description, it willbe deemed that the tone value takes on a value among the 256 steps of 0to 255 expressed by 8-bit data and the luminance is expressed in therange of 0% to 100% (the range from the minimum luminance to the maximumluminance that depends on the ability of the monitor or on a prescribedsetting).

In this case, as is illustrated in the graph of the FIGURE, the minimumtone value of 0 and the minimum luminance of 0% coincide (origin O ofthe graph) and the maximum tone value of 255 and the maximum luminanceof 100% coincide (point P of the graph). This is because a circuit ofmonitor 100 (normally, a circuit on the graphics board) is set so thatdisplay at the minimum luminance of 0% is performed when data indicatingthe minimum tone value of 0 is input and display at the maximumluminance of 100% is performed when data indicating the maximum tonevalue of 255 is input. However, the relationship of tone values andluminance values in between will not necessarily be a linearrelationship. This depends on the characteristics of a D/A conversioncircuit on the graphics board and the tone reproduction characteristicsnormally differ according to the type of each individual monitor, andmore strictly speaking, according to each individual lot.

It is known that with a general CRT monitor, the graph indicating thetone reproduction characteristics can be approximated by the functioncurve, “luminance=(tone value)^(γ)” having the power term, γ. WithWindows (registered trade mark), this γ value is recommended to be setto 2.2 in accordance with the “IEC 61966-2-1: Colour Measurement andManagement in Multimedia Systems and Equipment—Part 2-1: Default RGBColour Space—sRGB” standard. Also, with Macintosh (registered trademark), since there are many applications wherein printing data aredisplayed on a monitor, it is recommended that a value of 1.8, which isclose to the tone reproduction characteristics of printing, is used.Curve A, indicated in the FIGURE by the alternate long and short dashline, indicates the tone reproduction characteristics when γ=2.2.However, curves unique to each individual monitor, such as curves B andC, indicated in the FIGURE by solid lines, are obtained in actuality.Thus when data indicating a tone value of 186 is provided from thepersonal computer 200 to the monitor 100, a monitor with idealcharacteristics, such as indicated by curve A, will provide a luminancevalue of 50%, which is the ordinate value of point Q1. However, withactual monitors having characteristics indicated by curves B and C,luminance values corresponding to the ordinate values of points Q2 andQ3 are obtained respectively. Put in another way, in order to make amonitor having the characteristics indicated by curve B perform displayat the proper luminance of 50% in correspondence to a tone value of 186,a process of correcting the tone value of 186 to a tone value of 150,which corresponds to being the abscissa value of the point Q4, must beperformed, and in order to make a monitor having the characteristicsindicated by curve C perform display at the proper luminance of 50% incorrespondence to a tone value of 186, a process of correcting the tonevalue of 186 to a tone value of 200, which corresponds to being theabscissa value of the point Q5, must be performed.

Such correction is generally referred to as gamma correction.Consequently, in using monitor 100 upon connection to personal computer200, etc., a graph indicating the tone reproduction characteristicsunique to this monitor 100 must be determined as monitor profile data inadvance and gamma correction using these data must be performed.

Though as mentioned above, there are methods of using optical measuringdevices among methods of measuring the tone reproduction characteristicsof each individual monitor, normally, a method of obtainingcharacteristics data while performing visual recognition with human eyesis employed. FIGS. 3A and 3B are plan views illustrating the generalprinciples of measuring tone reproduction characteristics by visualrecognition. With this method, first, a test pattern, such as that shownin FIG. 3A is made to be displayed on the screen of monitor 100 to bemeasured. This test pattern is made up of a first attribute region 10and a second attribute region 20. In the illustrated example, firstattribute region 10 is a square region and second attribute region 20 isa frame-like region that surrounds this square region. A uniform, evenpattern is made to be displayed in first attribute region 10, and areference pattern, having a prescribed reference luminance, is made tobe displayed in second attribute region 20.

As mentioned above, regardless of the curve that indicates the gammacharacteristics, the respective ends of the curve are fixed at thepoints O and P. That is, a region that is provided with data indicatingthe minimum tone value of 0 is always displayed at the lowest luminanceof 0% (totally black) and a region that is provided with data indicatingthe maximum tone value of 255 is always displayed at the highestluminance of 100% (totally white). Using this property, a referencepattern with a reference luminance that will serve as a basis isdisplayed in second attribute region 20.

FIG. 3B is a partially enlarged view of second attribute region 20. Asillustrated, second attribute region 20 is arranged by alternatinglypositioning stripe-like first sub-regions 21 with the minimum tone valueof 0 and stripe-like second sub-regions 22 with the maximum tone valueof 255. That is, a pattern of a black-and-white stripe design is formed.Here, if the area ratio of first sub-regions 21 and second sub-regions22 is set to 1:1 (in other words, if the widths of all of the black andwhite stripes set to be equal), even though the individual sub-regions21 and 22 are displayed at the lowest luminance of 0% or the highestluminance of 100%, when observed visually from a certain distance, theregion will be falsely recognized as being displayed at a luminance of50%. Obviously, for this purpose, the width dimensions of the black andwhite stripes must be made small to some degree so that it will bedifficult for the naked eye to observe the stripe pattern itself.

Thus in the pattern shown in FIG. 3A, second attribute region 20, whichforms the peripheral frame region, functions as a reference pattern thatsimulates a luminance of 50%. Meanwhile, an uniform, even pattern (inother words, a pattern wherein all pixels have the same tone value) isdisplayed in first attribute region 10 and the brightness thereof ismade adjustable by an input operation by the operator. Then while makingthe operator view this test pattern, the operator is made to perform anoperation of adjusting the tone value of the pixels in first attributeregion 10 so that the brightness of first attribute region 10 becomesthe same as the brightness of second attribute region 20.

Here, if, for example, the brightness of regions 10 and 20 become thesame when the tone value of the pixels inside first attribute region 10is set to 85, it can be recognized that with this monitor, the tonevalue corresponding to a reference luminance of 50% is 85. As shown inthe graph of FIG. 4, a point Q, having the reference luminance value of50% and the corresponding tone value of 85 as the respective coordinatevalues, is then plotted, and the curve that smoothly joins the threepoints, O, Q, and P, is determined as the curve of the tone reproductioncharacteristics (gamma characteristics) that are to be determined. Sinceas mentioned above, the tone reproduction characteristics of a generalCRT monitor can be approximated by the function curve, “luminance=(tonevalue)^(γ),” a curve such as that shown in FIG. 4 can be determineduniquely if three points are determined. Consequently, in order to makethe monitor, having the characteristics shown in FIG. 4, perform adisplay corresponding to a luminance of 50%, data indicating a tonevalue of 85 is provided.

<<<Section 2. Basic Tone Reproduction Characteristics Measuring Methodby This Invention>>>

The above-described conventional method for measuring tone reproductioncharacteristics has the merit that measurements based on the visualrecognition of an operator is enabled and measurement results that matchthe sensitivity characteristics of human eyes can be obtained. However,with a color monitor used in DTP processes for preparing printed matter,etc., tone reproduction characteristics measurement of higher precisionare demanded and adequate measurement results cannot be providednecessarily by the conventional measuring method. Experiments by theinventor of this application have shown that it is difficult to makemeasurements of adequate precision especially on liquid crystal colordisplays and on CRT color monitors that have undergone ageddeterioration. A main reason for this is considered to be that, withcolor monitors, tone reproduction characteristics differ according tocolor.

Generally with a color monitor, since color image display using thethree primary colors of R, G, and B is carried out, a separate tonevalue must be designated for each of the three primary colors, R, G, andB. However, with the conventional tone reproduction characteristicmeasuring method, there is no concept of measuring separatecharacteristics according to color and all of the three primary colorsare handled together. For example, with a measurement using a testpattern such as that shown in FIG. 3A, brightness adjustment of theinterior of first attribute region 10 is performed under the premise ofalways using tone values in common for the three primary colors, R, G,and B. The tone reproduction characteristics obtained by theconventional method are thus characteristics in common to the threeprimary colors, R, G, and B, and when tone reproduction characteristicssuch as those shown in FIG. 4 are obtained, the same characteristics areused to perform gamma correction on all of the three primary colors, R,G, and B.

This was done conventionally since with a general color monitor, it wasconsidered that the tone reproduction characteristics are substantiallythe same for the three primary colors, R, G, and B. Indeed in the caseof CRT color monitors, adjustments are made so that the tonereproduction characteristics of the primary colors, R, G, and B will besubstantially the same at the time of product shipment. However, sincefluorescent materials undergo degradation due to aged deterioration, thetone reproduction characteristics come to differ according to eachprimary color. Also in the case of a general liquid crystal colordisplay, the tone reproduction characteristics differ according to eachprimary color already at the time of product shipment.

As a result of actually using an optical measuring device and measuringthe tone reproduction characteristics according to each primary color ofa variety of CRT color monitors and liquid crystal displays made by avariety of manufacturers, the present inventor has found certain trendsin common for liquid crystal displays, regardless of old or new and formany of second-hand CRT color monitors. These trends show that, for thethree primary colors, R, G, and B, whereas substantially the same tonereproduction characteristics are obtained for the primary color R (red)and the primary color G (green), different tone reproductioncharacteristics are obtained for the primary color B (blue). To be morespecific, for many liquid crystal color monitors, tone reproductioncharacteristics of the trends shown in FIG. 5 are obtained. In theillustrated example, curves Cr, Cg, and Cb are the tone reproductioncharacteristics that are measured for the primary colors R, G, and B,respectively. Though curves Cr and Cg are the same, curve Cb is somewhatshifted upwards. Oppositely with second-hand CRT color monitors, justcurve Cb is somewhat shifted downwards.

Though the reason as to why such common trends appear has not yet beenanalyzed theoretically, in view that the same trends are seemed to beseen with all models of all manufacturers, these trends can beconsidered to be universal trends that are seen substantially in commonamong color monitors using the three primary colors R, G, and B. Theinventor considers that in the case of liquid crystal color monitors,the above trend appears due to the properties of the liquid crystalmaterial and the optical characteristics of the polarizing plate, andconsiders that in the case of second-hand CRT color monitors, the abovetrend appears due to the degradation of the fluorescent material forblue being more severe than the degradations of the fluorescentmaterials for red and green. Consequently, as shown in the FIG. 5, inorder to make a color monitor perform a gray display of a luminance of50%, 85, which is the abscissa value of the points Qr and Qg, must beprovided as the tone value for the primary colors R and G, whileproviding 46, which is the abscissa value of point Qb, as the tone valuefor the primary color B.

The basic philosophy of this invention is to determine tone reproductioncharacteristics according to each of the three primary colors, R, G, andB, separately and independently or at least determine tone reproductioncharacteristics for the primary colors R and G and tone reproductioncharacteristics for the primary color B separately and independently onthe basis of the above facts to enable tone reproduction characteristicsto be measured at high precision.

The tone reproduction characteristics measuring device for color monitorof the present invention is a device for determining, by visualrecognition, the tone reproduction characteristics, which indicate therelationship between input signal tone values and actual displayluminance, of a color monitor having a function of displaying colorimages using the three primary colors, R, G, and B, and as with theconventional measuring method described in Section 1, the basicprinciple thereof is to use a test pattern such as that shown in FIG.3A. However, in order to determine different tone reproductioncharacteristics according to color, the following measures are takenwith this invention.

That is, an even pattern of uniform brightness and color is made to bedisplayed at all times in first attribute region 10, and the brightnessand color of this even pattern are varied based on operations of anoperator or varied automatically based on prescribed rules. This methodis new in that not just the variation of brightness but the variation ofcolor, which is not carried out in conventional methods, is carried out.The operator then compares first attribute region 10 and secondattribute region 20 visually and continues varying the brightness andcolor in regard to first attribute region 10 until it is recognized thatboth regions are matched in brightness and color.

Though this variation of brightness and variation of color can, inprinciple, be carried out simultaneously, for practical use, preferablya brightness varying operation and a color varying operation arearranged to be performed separately and independently and the operatoris made to perform recognition of the matching of brightness during thebrightness varying operation and perform recognition of the matching ofcolor during the color varying operation.

The brightness varying operation can be performed by a task ofincreasing or decreasing the tone values of all of the three primarycolors, R, G, and B, by a common variation amount. For example, when ina state wherein a prescribed even pattern is displayed in firstattribute region 10 using the tone values, R=120, G=120, and B=120, ifeach tone value is increased by a common variation amount S=5, the tonevalues become R=125, G=125, and B=125, and the luminance of the evenpattern displayed in first attribute region 10 is thus increasedslightly. Oppositely, by decreasing each tone value by the commonvariation amount S=5, the tone values become R=115, G=115, and B=115,and the luminance of the even pattern displayed in first attributeregion 10 is thus decreased slightly. Such a brightness varyingoperation can be said to be mainly an operation of varying thebrightness of an even pattern without hardly giving rise to a colorvariation that can be recognized visually (though strictly speaking,there is a possibility that a color variation will be recognized).

Meanwhile, the color varying operation can be performed by a task ofincreasing or decreasing the tone value of one of the three primarycolors, R, G, and B. For example, when in a state wherein a prescribedeven pattern is displayed in first attribute region 10 using the tonevalues, R=120, G=120, and B=120, the tone value concerning a specificcolor R is increased by just a variation amount S=5, the tone valuesbecome R=125, G=120 and B=120 and the redness of the even patterndisplayed in first attribute region 10 can thus be strengthenedslightly. Oppositely, by performing by decreasing by the variationamount S=5, the tone values become R=115, G=120, and B=120, and theredness of the even pattern displayed in first attribute region 10 canthus be weakened slightly. With such a color varying operation, there islittle variation of brightness that can be recognized visually and theoperation can be said to be mainly an operation of varying the color ofan even pattern.

In order to vary tone values based on operation inputs by the operator,an operation panel, such as that shown in FIG. 6, is made to bedisplayed on the screen to enable adjustment of the tone values of therespective primary colors by mouse operation, etc., by the operator.With this operation panel, the brightness varying operation and thecolor varying operation can be performed separately and independently.That is, each of the four horizontal bars that make up this operationpanel is a bar indicating a certain tone value within the range of 0 to255, and the right end position of the bar with the hatching indicatesthe certain tone value. The right end position of each bar can bemodified instantly to a position that is clicked by a mouse cursor M,and the operator can set the right end positions of the four bars at anyarbitrary position.

The bars indicated as “R,” “G,” and “B” in the FIGURE are bars forsetting the tone values of the primary colors, R, G, and B,respectively. Meanwhile, the bar indicated as “Brightness” is a bar thatconstantly indicates the average of the tone values of the primarycolors, R, G, and B, at that point. Thus when a tone value of any of thebars indicated as “R,” “G,” and “B” is modified (modification of theright end position), the tone value of the bar indicated as “Brightness”is also modified instantly in conjunction. Oppositely, when tone valueof the bar indicated as “Brightness” is modified, the tone values of therespective bars indicated as “R,” “G,” and “B” are modified instantly inconjunction by amounts that are in accordance with the modification (forexample, the variation amount with respect to the “Brightness” bar maybe distributed in accordance with proportional ratios that correspond tothe tone values of the respective bars).

By using such an operation panel, the operator performs the operation ofmodifying the tone value of the bar indicated as “Brightness” to performthe brightness varying operation and performs the operation of modifyingthe tone values of any of the bars indicated as “R,” “G,” and “B” toperform the color varying operation. For example, to perform a varyingoperation of making the brightness brighter, a position further to theright of the right end of the bar indicated as “Brightness” is clickedby the mouse, and to perform a varying operation of weakening theredness slightly, a position slightly to the left of the right end ofthe bar indicated as “R” is clicked by the mouse.

By making the operation panel shown in FIG. 6 be displayed near the testpattern shown in FIG. 3A and making the operator perform the brightnessvarying operation and color varying operation to thereby performadjustment to make first attribute region 10 and second attribute region20 be matched in brightness and color, the tone reproductioncharacteristics of each primary color of the three primary colors, R, G,and B, can be determined separately and independently. For example,consider a case where, in the state in which a reference patterncorresponding to a luminance of 50% is displayed inside second attributeregion 20, the operator recognizes that the regions are matched both inbrightness and color. The operator is then made to click on a matchbutton 30 when the matching of both the brightness and the color arethus recognized. If at this point, the tone values indicated by therespective bars indicated as “R,” “G,” and “B” in the operation panelshown in FIG. 6 are R=85, G=85, and B=46, curves Cr, Cg, and Cb, showingthe tone reproduction characteristics of the respective primary colors,are obtained as shown in FIG. 5.

However, in terms of practical use, the operations of varying the tonevalues using the operation panel shown in FIG. 6 are difficult toperform unless the operator is an expert. This is because though ageneral operator can recognize that “first attribute region 10 andsecond attribute region 20 differ slightly in color,” he/she cannot makethe judgment of “which color component among the three primary colorsshould be increased or decreased to obtain the same color.” Thus in thecase where a measurement using the operation panel shown in FIG. 6 iscarried out, though tone reproduction characteristics can be determinedfor all of the three primary colors, R, G, and B separately andindependently, a burden in terms of measurement operation is placed onthe operator. The root cause is that the four parameters of brightness,the primary color R, primary color G, and primary color B are theobjects of adjustment.

The present inventor has thus conceived a practical operation panel,which is shown in FIG. 7. This operation panel has four adjustingbuttons 31 to 34 and a match button 30. The four adjusting buttons 31 to34 are positioned so that when a two-dimensional XY coordinate system,such as illustrated on the plane on which the respective buttons arepositioned, is defined (such a coordinate system is not displayed on theactual operation panel), first button 31 and second button 32 arepositioned at opposing positions along the X-axis that sandwich theorigin, and third button 33 and fourth button 34 are positioned atopposing positions along the Y-axis that sandwich the origin. Though thefour adjusting buttons 31 to 34 have triangular shapes in this example,these do not need to be triangular in shape.

Here, first button 31 is a button that provides an instruction of makingthe even pattern displayed inside first attribute region 10 brighter,second button 32 is a button that provides an instruction of making theeven pattern darker, third button 33 is a button that provides aninstruction of strengthening the component of a specific color of theeven pattern, and fourth button 34 is a button that provides aninstruction of weakening the component of a specific color of the evenpattern. In the present example, the primary color B is set as thespecific color.

The relationship between the operations of the respective buttons andthe operation of varying the tone values of the respective primarycolors is as follows. First, when there is an operation input (forexample, a mouse click) for first button 31, an operation of adding acommon variation amount to all of the tone values of the three primarycolors, R, G, and B is performed, and when there is an operation inputfor second button 32, an operation of subtracting the common variationamount from all of the tone values of the three primary colors, R, G,and B is performed. When there is an operation input for third button33, an operation of adding a prescribed variation amount to the tonevalue of the specific color (the primary color B in the present example)is performed, and when there is an operation input for fourth button 34,an operation of subtracting the prescribed variation amount from thetone value of the specific color is performed.

For example, when the variation amount S is set to 5, each time firstbutton 31 is clicked, a modification of increasing all tone values ofthe three primary colors, R, G, and B by just 5 is performed, and eachtime second button 32 is clicked, a modification of decreasing all tonevalues of the three primary colors, R, G, and B by just 5 is performed.Likewise, each time third button 33 is clicked, a modification ofincreasing the tone value of just the primary color B, which is thespecific color, by just 5 is performed, and each time fourth button 34is clicked, a modification of decreasing the tone value of just theprimary color B by just 5 is performed. Obviously, since the allowablerange of the respective tone values is 0 to 255, modifications beyondthe minimum tone value of 0 and the maximum tone value of 255 cannot beperformed.

The object of adjustment in the operation panel shown in FIG. 7 willthus be just the two parameters of brightness and the primary color B.Moreover, since the operation system is one where the adjustment of thebrightness parameter is performed by operations in the X-axis directionand the adjustment of the primary color B parameter is performed byoperations in the Y-axis direction and these can thus be graspedintuitively, the operability is improved extremely in comparison to theoperation panel shown in FIG. 6. First button 31 and second button 32are buttons for performing the brightness varying operation wherein thetone values are varied primarily so that the brightness of the evenpattern will change, and third button 33 and fourth button 34 arebuttons for performing the color varying operation wherein a tone valueis varied primarily so that the color of the even pattern will change.

The characters of “Bright,” “Dark,” “Blue,” and “Yellow” are indicatednear the respective buttons 31 to 34 to provide an intuitive guidelineto the operator. That is, the operator clicks first button 31 to make amodification of making the pattern brighter, clicks second button 32 tomake a modification of making the pattern darker, clicks third button 33to make the pattern bluer (increase the blue component), and clicksfourth button 34 to make the pattern more yellow (decrease the bluecomponent). And in the final stage when it is recognized that matchingof both brightness and color is achieved, match button 30 is clicked.

With the operation panel shown in FIG. 7, the tone values of therespective three primary colors, R, G, and B cannot be set independentlyof each other and the tone values of the primary color R and the primarycolor G will constantly be the same. Thus not all of the tone valuereproduction characteristics of the three primary colors R, G, and B canbe determined separately and independently according to the primarycolors. However, since the tone value of primary color B, which is setas the specific color, can be set to differ from the tone values of theother primary colors R and G, it is possible to determine the tonereproduction characteristics of the primary colors R and G and the tonereproduction characteristics of the primary color B separately andindependently.

As was described above based on the graph of FIG. 5, with many colormonitors, whereas substantially the same tone reproductioncharacteristics are obtained for the primary color R and the primarycolor G among the three primary colors, R, G, and B, different tonereproduction characteristics are obtained for the primary color B. Thusif it is premised that characteristics are to measured for a colormonitor with such trends, problems in terms of practical use will notarise even when tone value varying operations are performed by theoperation panel shown in FIG. 7. That is, with the operation panel shownin FIG. 7, the primary color B is set as the specific color among thethree primary colors, R, G, and B, and a curve indicating the tonereproduction characteristics for the primary color B and a curveindicating the tone reproduction characteristics in common for theprimary colors R and G can be determined separately.

The variation amount S, by which a tone value is increased or decreasedby the clicking of a button, may be made switchable in an arbitrarymanner. For example, a method may be employed wherein a rough adjustmentsetting with the variation amount S=5 and fine adjustment setting withthe variation amount S=1 are provided, a rough tone value varyingoperation is performed with the rough adjustment setting in the initialstages, and the fine adjustment setting is switched to at the point atwhich the brightness and color are recognized as having become close tosome degree to continue with a fine tone value varying operation usingthe fine variation amount.

It is also possible to provide an arrangement wherein the variationamount is changed according to the location of clicking of each button.For example, if an arrangement is made so that when a tip portion(portion away from the origin of the XY coordinate system) of thetriangular shape that makes up each of buttons 31 to 34 is clicked, atone value varying operation of a large variation amount (for example,of the variation amount S=5) will be performed, and when a base portion(portion close to the origin of the XY coordinate system) of thetriangular shape is clicked, a tone value varying operation of a smallvariation amount (for example, of the variation amount S=1) will beperformed, the operator will be enabled to perform the measurement tasksefficiently by performing clicking operations suitably in accordancewith the required variation amounts.

<<<Section 3. Automatic Tone Value Varying Method>>>

In Section 2 above, an example was described wherein tone value varyingoperations are performed by making the operator perform operation inputsfor varying the brightness and color using an operation panel such asshown in FIG. 6 or 7. In particular, by using the operation panel shownin FIG. 7, since just adjustment operations concerning the twoparameters of bright/dark and bluish/yellowish need to be performed, thework load of the operator is lightened significantly in comparison tothe case of using the operation panel shown in FIG. 6. However,regardless of which operation panel is used, the operator him/herselfmust perform operation inputs in directions in which the brightness andcolor will become matched.

Here, a method of lightening the burden of such operation inputs furtherwill be described. The main features of this method are that the tonevalues of the even pattern displayed inside first attribute region 10are made to vary automatically with time in accordance with prescribedrules that are established in advance and the operator is made to make anotification by clicking a match button, etc., when he/she recognizesthat the brightness and color of the even pattern match those of thereference pattern. Here, the rules for automatically varying the tonevalues with time may be any rules as long as they are rules by which thebrightness and color will vary within the required ranges, for practicaluse, rules by which the two types of varying operations of thebrightness varying operation and the color varying operation areexecuted separately are preferable.

Specifically, arrangements are made to perform the two types of varyingoperation of the brightness varying operation, wherein a commonvariation amount is added to or subtracted from all of the respectivetone values of the three primary colors, R, G, and B, at a prescribedtiming to thereby change the tone values so that mainly the brightnessof the even pattern changes, and the color varying operation, wherein aprescribed variation amount is added to or subtracted from the tonevalue of one specific color among the three primary colors, R, G, and B(as mentioned above, for practical use, the primary color B ispreferably set as the specific color) at a prescribed timing to therebychange the tone value so that mainly the color of the even patternchanges.

The above-described brightness varying operation corresponds toautomatically clicking first button 31 or second button 32 of theoperation panel shown in FIG. 7 at the prescribed timing. For example,if a common variation amount S=+5 (+ indicates that the tone values areto be increased) is set and a repetition cycle of 1 second is set as theprescribed timing, all of the respective tone values of the threeprimary colors, R, G, and B are increased by 5 automatically every 1second. Or, if a common variation amount S=−6 (− indicates that the tonevalues are to be decreased) is set and a repetition cycle of 2 secondsis set as the prescribed timing, all of the respective tone values ofthe three primary colors, R, G, and B are decreased by 6 automaticallyevery 2 seconds.

Since the respective tone values can only take on values within theallowable range of 0 to 255, when the tone value obtained by the varyingoperation of adding the variation amount exceeds the maximum tone valueof 255, a circulation process of incrementing the minimum tone value of0 by the excess amount is performed, and when the tone value obtained bythe varying operation of subtracting a variation amount falls below theminimum tone value of 0, a circulation process of decrementing themaximum tone value of 255 by the excess amount is performed. Forexample, though when a variation amount of 5 is added to a tone value of253, the tone value will be 258, in this case, the tone value of 2,which is obtained by subtracting 256, is used instead. That is,circulation of the tone values in the manner of 255→0 is performed sothat the tone value for the excess 3 steps is counted as 0, 1, 2, fromthe minimum tone value of 0. Likewise, though in the case where thevariation amount of 6 is subtracted from a tone value of 2, thesubtraction result is −4, the tone value of 252, which is obtained byadding 256, is used instead. That is, circulation of the tone values inthe manner of 0→255 is performed so that the tone value for the excess 4steps is counted as 255, 254, 253, 252, from the maximum tone value of255.

Though the initial tone values of the respective primary colors in sucha brightness varying operation may be set arbitrarily, for practicaluse, the initial tone values of the three primary colors are set to aprescribed common value. For example, when R=0, G=0, and B=0 are set asinitial values and variation by a common variation amount S=+5 isperformed, the tone value of each primary color will vary automaticallyin the manner of 0→5→10→15→ . . . 250→255→4→9→14→ . . . . When such avarying operation is performed automatically, the even pattern insidefirst attribute region 10 will be observed by the operator as varyingwith time in the manner of totally black→dark gray→intermediategray→light gray→white→totally black→ . . . . Since the reference patternof a luminance of 50% is displayed inside second attribute region 20,the operator will recognize that the even pattern is matched inbrightness with the reference pattern at the point at which the evenpattern becomes an intermediate gray. The operator is made to performthe input indicating the matching of brightness (for example, theclicking of a brightness match button) at the point of recognizing thatthe brightness is matched.

Needless to say, since this operation is performed by a human being, thedecision of recognition of matching may be delayed and thus the timingat which the matching input operation is performed may be missed. Inthis case, though the even pattern will go past intermediate gray andchange to becoming light gray, it will eventually circulate back to theblack state and the opportunity for performing the matching inputoperation for intermediate gray will arrive again. By thus employing amethod of varying the tone values in a repeatedly circulating manner,the operator is provided with the opportunity of performing the matchinginput operation several times and a more accurate matching input canthus be anticipated. Actually, after a few times of circulation, theoperator will come to sensually grasp the cycle of tone change and willfinally able to perform an accurate matching input operation.

If the varying amount S is set to a somewhat large value, there may becases where the operator will not be able to visually recognize completematching. In this case, the operator is made to perform the inputindicating the recognition of matching when the patterns become closestto each other. This applies not just to the recognition of matching ofbrightness but also to the recognition of matching of color as will bedescribed below. That is, with the present invention, “recognition ofmatching” by an operator does not necessarily mean the recognition ofcomplete matching but covers the range of recognition wherein, underprescribed conditions, it is judged that the brightness and color of thepatterns have become closest. In actuality, matching is recognized whenthe contour of first attribute region 10 appears to have become embeddedand dissolved inside second attribute region 20.

Though the brightness varying operation has been described above, thecolor varying operation is nearly the same. The color varying operationcorresponds to automatically clicking third button 33 or fourth button34 of the operation panel shown in FIG. 7 at the prescribed timing. Forexample, if a common variation amount S=+5 is set and a repetition cycleof 1 second is set as the prescribed timing, just the tone value of thespecific color among the three primary colors, R, G, and B is increasedby 5 automatically every 1 second. If the primary color B is set as thespecific color, the color of the even pattern will gradually increase inblueness. Needless to say, since a circulation process is performed sothat the tone value will remain within the allowed range of 0 to 255 inthis color varying operation as well, immediately after the state ofmaximum blueness is reached, the state of maximum yellowness (minimumblueness) is entered. The tone values of the primary colors R and G arekept fixed.

When the color varying operation is thus performed automatically, theeven pattern inside first attribute region 10 will be observed by theoperator to circulate in the manner of gradually lessening in yellownessfrom a color strong in yellowness, then after becoming nearlyachromatic, gradually becoming stronger in blueness, and then afterreaching the state of maximum blueness, returning to the color strong inyellowness. Since the achromatic reference pattern of a luminance of 50%is displayed inside second attribute region 20, the operator willrecognize the matching of color with the reference pattern at around thepoint at which the extremely pale color of the even pattern changes frombeing yellowish to being bluish. The operator is made to perform aninput indicating the matching of color (for example, the clicking of acolor match button) at the point of recognizing the matching of color.

Since this judgment of color matching will also be an extremely delicatesensory judgment on the part of the operator, the operator may miss thetiming at which the matching input operation is to be performed.However, as with the transition of brightness, the transition of coloris also circulated and performed repeatedly, the opportunity forperforming the matching input operation will arrive repeatedly so thatan accurate matching input operation will be enabled in the final stage.

FIG. 8 is a diagram showing an example of an operation panel used formaking the operator perform the brightness matching input operation andthe color matching input operation while the brightness varyingoperation and the color varying operation are executed automaticallybased on prescribed rules in accordance with the above-describedprinciples. As illustrated, the buttons operated by the operator are thethree types of a start button 40, brightness match button 41, and colormatch button 42, and at the sides of the respective buttons are providedexplanatory texts for the respective operations. By making an operationpanel such as shown in FIG. 8 be displayed near the test pattern shownin FIG. 3A and making the operator click the respective buttons using amouse, etc., the series of measurement tasks are completed.

That is, first, the operator clicks start button 40 in accordance withthe explanatory text indicated as “Step 0.” The above-describedautomatic brightness varying operation is thereby executed and thebrightness of the even pattern inside first attribute region 10 beginsto vary with time. Then in accordance with the explanatory textindicated as “Step 1,” the operator clicks brightness match button 41 atthe point at which he/she feels that the brightness of the even patternhas become the same as the brightness of the reference pattern. Theabove-described automatic color varying operation is then executed, andthe color (the color in regard to the primary color B) of the evenpattern begins to vary with time. Then in accordance with theexplanatory text indicated as “Step 2,” the operator clicks color matchbutton 42 at the point at which he/she feels that the color of the evenpattern has become the same as the color of the reference pattern.

The series of measurement tasks are completed by the above procedure.Each of the respective tone values of the three primary colors, R, G,and B at the point at which color match button 42 has been clicked (inthe case of this example, the values for R and G will be the same), isthen deemed to be the tone value of the corresponding primary color forthe reference luminance of 50% and plotted as point Q in FIG. 4 and thetone reproduction characteristics curve is determined for each primarycolor (the curves for R and G will be the same).

Brightness match button 41 shown in FIG. 8 thus functions as abrightness coincidence signal input means for inputting a brightnesscoincidence signal that indicates that the operator has recognized thematching of brightness while performing the brightness varyingoperation, and color match button 42 functions as a color coincidencesignal input means for inputting a color coincidence signal thatindicates that the operator has recognized the matching of color whileperforming the color varying operation. And when the inputs of both thebrightness coincidence signal and the color coincidence signal arecompleted, it is deemed that a coincidence signal, indicating therecognition that both the brightness and the color are matched, is inputand the tone reproduction characteristics are determined according tothe respective primary colors. In the above-described example, theprimary color B, among the three primary colors, R, G, and B, is set asthe specific color and a curve indicating the tone reproductioncharacteristics of the primary color B and a curve indicating the commontone reproduction characteristics of the primary colors R and G aredetermined separately of each other.

Though with the example using the operation panel shown in FIG. 8, theinput operation of the brightness coincidence signal and the inputoperation of the color coincidence signal are performed once each tocomplete the measurement tasks, for practical use, an embodiment whereinsuch operations are executed repeatedly in alternation is preferable. Afirst reason for this is that the matching recognition operation is asensory operation based on human vision and it may not be possible toperform recognition accurately with a single input operation. Secondly,the brightness varying operation is not necessarily an operation ofvarying just the brightness and the color varying operation is notnecessarily an operation of varying just the color. For example, withthe operation panel of FIG. 8, even if the brightness is matchedaccurately at the point at which brightness match button 41 is clicked,since not just the color but the brightness is also be varied by thesubsequently executed color varying operation, the brightness-matchedstate will be disrupted. In order to avoid such a problem, it iseffective to execute the brightness matching operation and colormatching operation repeatedly in alternation and it is especiallyeffective to execute the operations repeatedly while graduallydecreasing the tone value variation amount.

Specifically, the process illustrated by the flowchart of FIG. 9 isperformed. First in step S1, the initial values of the respective tonevalues of the three primary colors R, G, and B and the initial value ofthe variation amount S is set. In the illustrated example, therespective values are set to R0, G0, B0, and S0.

Then in steps S2 and S3, the operation of matching the brightness isexecuted. That is, in step S2, the process of adding the variationamount S to each of the tone values of the three primary colors, R, G,and B is performed. However, since the above-described circulationprocess is performed, when a tone value exceeds 255, 256 is subtractedtherefrom. Then in step S3, whether or not the brightness match buttonhas been pressed is judged, and if it has not been pressed, a return tostep S2 is performed and the tone values are renewed. The processes ofsteps S2 and S3 are thus repeated until the brightness match button ispressed. Needless to say, the cycle of this repeated process is set forexample to every one second or other time period that is adequate forthe operator to make a matching recognition judgment.

If in step S3, the pressing of the brightness match button is detected,the operation of matching the color is executed in steps S4 and S5. Thatis, firstly in step S4, the process of adding the variation amount S tojust the tone value of the specific color B is performed. Since thecirculation process is performed here as well, when the tone valueexceeds 255, 256 is subtracted therefrom. Then in step S5, whether ornot the color match button (which may be used in common as thebrightness match button as well) has been pressed is judged, and if ithas not been pressed, a return to step S4 is performed and the tonevalue of the specific color B is renewed. The processes of steps S4 andS5 are thus repeated until the color match button is pressed. The cycleof this repeated process is also set for example to every one second orother time period that is adequate for the operator to make a matchingrecognition judgment.

If in step S5, the pressing of the color match button is detected,though this means that both the brightness coincidence signal and thecolor coincidence signal have been input tentatively from the operator,the finalization of the tone values that are to be the measurementresults is not performed at this point, and the procedures from step S2onwards are executed again via step S6 and step S7. Moreover, in stepS7, a renewal process of decreasing the variation amount S is executed.The variation amount S that is added in steps S2 and S4 in the secondround is smaller than the value used in the first round, thus enablingfiner judgment of matching. The process is repeated three times, fourtimes, etc., as necessary while making the variation amount S evensmaller.

For example, in the case where the initial value S0 of the variationamount S is set to +5, this is renewed by decreasing by 2 at a time instep S7, and the specified value of the variation amount S for step S6is set to 1, the variation amount S=+5 in the first round, the variationamount S=+3 in the second round, the variation amount S=+1 in the thirdround, and after the third time around, the repeated process iscompleted. When the variation amount S has reached the specified valuethat had been set in advance, step S8 is entered from step S6 and therespective tone values of the three primary colors, R, G, and B, at thatpoint are output. These tone values are used as the corresponding tonevalues corresponding to a reference luminance of 50% to determine thetone reproduction characteristics according to the respective primarycolors as described above.

With the procedure in FIG. 9, the recognition of matching in the firstround and the recognition of matching in the second round differ greatlyin recognition conditions. For example, though the recognition ofmatching in step S3 in the first round indicates that the brightness hastentatively reached a matched state of some level, the matching of coloris not considered at all at that point. However, in the recognition ofmatching in step S3 in the second round, since the recognition ofbrightness matching is premised on the completion of the recognition ofcolor matching in step S5 of the first round, a more preferable matchingstate will be obtained in terms of the essential purpose of matchingboth the brightness and the color. Also, since the variation amount S isdecreased to enable finer recognition of matching on each successiveround, an even more preferable matching state will be obtained by therecognition of matching in step S3 of the third round than by therecognition of matching in step S3 of the second round.

The procedure illustrated by the flowchart of FIG. 9 can thus be said tobe a process wherein, when in the state of performing the brightnessvarying operation (step S2), the brightness coincidence signal is input(step S3), the color varying operation is started (step S4), and when inthe state of performing this color varying operation (step S4), thecolor coincidence signal is input (step S5), the brightness varyingoperation (step S2) is started, and the brightness varying operation andcolor varying operation are executed repeatedly in alternation whilegradually decreasing the variation amount S of the tone values (stepS7). And when the input of both the brightness coincidence signal andthe color coincidence signal is completed after the variation amount Shas reached the prescribed specific value, it is deemed that thecoincidence signal indicating the recognition that both the brightnessand the color are matched is input.

A negative value may be set as the variation amount S. In this case,since the tone values after variation are practically determined bysubtraction in steps S2 and S4, a process of adding 256 is performedwhen the tone value after variation becomes a negative value. Needlessto say, in step S7, renewal is performed so that the absolute value ofthe variation amount S decreases gradually.

Though in the above-described embodiment, the repeated variation of thetone values is performed as a circulating motion of 0˜255→0˜255→0˜255 .. . , this repeated variation of the tone values may be a reciprocatingmotion instead. In this case, at the point at which a varied value thatexceeds or falls below the maximum tone value or minimum tone value isobtained, a fold-back process is performed and the sign of the variationamount S is inverted. Specifically, when as a result of increasing atone value gradually by a positive variation amount +S, the maximum tonevalue of 255 is exceeded, the sign of the variation amount is invertedand the tone value is decreased gradually by the negative variationamount −S, and when consequently the tone value falls below the minimumtone value of 0, the sign of the variation amount is inverted and thetone value is increased gradually again by the positive variation amount+S. A process of gradually increasing the tone value from 0 to 255 and aprocess of gradually decreasing the tone value from 255 to 0 are thusperformed in alternation.

Furthermore, though in above-described examples, regardless ofperforming the repeated variation of the tone values in the form ofcirculating motion or reciprocating motion, the tone values are variedover the entire allowable range of 0 to 255, for practical use,variation over this entire range is not necessary. For example, in thecase where the tone reproduction characteristics of the monitor, whichis the object of measurement, exhibit the curves shown in FIG. 5, thetone values of R=85, G=85, and B=46 will be obtained in the final stageas the corresponding tone values corresponding to a reference luminanceof 50%. These values are considerably biased towards the 0 side withrespect to the central value of 128 of the range of 0 to 255. However,with a general monitor, it is quite unlikely in practical terms thatvalues such as 10 and 20 or 240 and 250 will be obtained as thecorresponding tone values corresponding to a reference luminance of 50%.Thus for practical use, the circulating motion or reciprocating motionmay be carried out in a limited range, such as 30 to 230.

Also in the case of performing processes repeatedly while graduallydecreasing the variation amount S as in the procedure illustrated inFIG. 9, more efficient measurement tasks will be enabled by narrowingthe range of variation of the tone values to be subject to circulatingmotion or reciprocating motion at the same time as decreasing thevariation amount S. For example, in steps S2 and S4 of the first roundin which the variation amount S is set to +5, the tone value variationrange is set to the entire allowable range of 0 to 255. Then in steps S2and S4 of the second round in which the variation amount S is set to +3,the tone value variation ranges are narrowed to the ranges of±30centered about the tone values prior to variation.

By doing so, if at the point at which the first round is ended, theresults, R=90, G=90, and B=50 are obtained, variations within thelimited ranges of R=60 to 120, G=60 to 120, and B=20 to 80 are performedin step S2 of the second round. Since roughly approximate values (thevalues of R=90, G=90, and B=50 in the present example) are obtained inthe first round processes as the tone values of the respective primarycolors for which the matching of brightness and color are anticipated,it can be said that it is adequate to perform variations within theranges of±30 centered about these roughly approximate values in thesecond round. It is inefficient to vary the tone values to values forwhich there is absolutely no possibility of matching. Likewise, in thethird round, for example, the variation amount S is set to +1 andvariations within ranges of±10 centered about the tone values prior tovariation are carried out.

<<<Section 4. Method of Plotting More Points>>>

As mentioned in Section 1, in order to determine tone reproductioncharacteristics as in the graph of FIG. 4, a point Q, besides therespective end points O and P of the graph, is plotted and anapproximate function curve that passes through the three points, O, P,and Q is determined by computation. Also as mentioned above, in order todetermine the position of point Q by measurement by visual recognition,a method is employed wherein a test pattern such as that shown in FIG.3A is used, a reference pattern, which is formed of black and whitestripes as shown in FIG. 3B and corresponds to a reference luminance of50%, is displayed inside second attribute 20, and the sameness withrespect to the even pattern inside first attribute region 10 isconfirmed visually.

The tone reproduction characteristics (gamma characteristics) can bedetermined as an approximate function curve that passes through thethree points O, P, and Q since it is known that the tone reproductioncharacteristics of a general CRT monitor is a function curve of theform, “luminance=(tone value)^(γ),” having the power term, γ. This isbecause, in the first place, the relationship “L=E^(γ),” holds betweenthe voltage E that is applied to a cathode ray tube and the emittedlight output L. Thus in the case of a monitor that uses a cathode raytube, it is sufficient to use a reference pattern corresponding to areference luminance of 50% to measure the corresponding tone value andplot the point Q. However, with a liquid crystal display, etc., the tonereproduction characteristics will not necessarily be a function curvehaving the power term, γ.

In the case where the curve of the tone reproduction characteristicscannot be approximated by a function curve having the power term, γ, itis difficult to determine an accurate approximate function curve justwith the three points of O, P, and Q. An example of determining tonereproduction characteristics that are expressed by an arbitrary functionby plotting more points on a graph will now be described. Specifically,an embodiment wherein three points, Q1, Q2, and Q3, are plotted besidesthe respective ends O and P of the graph as shown in FIG. 10 todetermine an approximate function curve that passes through the fivepoints, O, Q1, Q2, Q3, and P, by computation will now be described.

Firstly, point Q2 shown in FIG. 10 can be measured by the method thathas been described above. That is, the illustrated point Q2 can beplotted from the measurement result that the corresponding tone valuefor a reference luminance of 50% is 85. Such measurement is performedusing a test pattern, wherein a reference pattern that falsely exhibitsa luminance of 50% is displayed inside second attribute region 20 asshown in FIG. 3B, and performing the tone value varying processes formaking the even pattern displayed in first attribute region 10 becomematched in brightness and color to the reference pattern.

Meanwhile, to determine points Q1 and Q3, the reference luminance of thereference pattern displayed in second attribute region 20 is changed to25% and 75%, respectively, and then the measurement processes of exactlythe same procedures are carried out. With the example shown in FIG. 10,point Q1 is plotted in accordance with the measurement result that thecorresponding tone value for the reference luminance of 25% is 26 andpoint Q3 is plotted in accordance with the measurement result that thecorresponding tone value for the reference luminance of 75% is 148.Obviously in actuality, the corresponding tone values corresponding tothe reference luminance values of 25%, 50%, and 75% are determined foreach of the primary colors, and the respective points Q1, Q2, and Q3 areplotted for each primary color.

The reference luminance of the reference pattern can be set arbitrarilyby adjusting the area ratio of first sub-regions 21 and secondsub-regions 22. For example, the reference pattern shown in FIG. 3B isarranged as a black-and-white stripe pattern wherein stripe-like firstsub-regions 21, with the minimum tone value of 0, and second stripe-likesub-regions 22, with the maximum tone value of 255, are positioned inalternation, and since the area ratio of first sub-regions 21 to secondsub-regions 22 is set to 1:1, the reference luminance is 50%. By settingthis area ratio to 3:1 (for example, by setting the width of each blackband to be three times that of each white band), the reference patternwith a reference luminance of 25% can be realized, and by setting thisarea ratio to 1:3 (for example, by setting the width of each black bandto be ⅓rd that of each white band), the reference pattern with areference luminance of 75% can be realized.

Generally, N reference patterns of mutually different referenceluminance can be formed by setting a plurality (N) of area ratios forfirst sub-regions 21 and second sub-regions 22. By the operatorperforming the visual recognition measurement tasks as described aboveon N test patterns using such N types of reference patterns, Ncorresponding tone values corresponding to the respective referenceluminance values are obtained. Then as shown in FIG. 10, upon defining atwo-dimensional coordinate system, having the tone value as a firstcoordinate axis (abscissa) and the luminance as a second coordinate axis(ordinate), N points (the three points Q1, Q2, and Q3 in the case of theexample of FIG. 10), having the respective reference luminance valuesand corresponding tone values as the coordinate values, are plotted ontothis coordinate system, the point having the minimum luminance value andminimum tone value as the coordinate values (the origin O in the case ofthe example FIG. 10) and the point having the maximum luminance valueand maximum tone value as the coordinate values (the point P in the caseof the example FIG. 10) are plotted, and a curve passing through thetotal of (N+2) plotted points is determined as the curve indicating thetone reproduction characteristics, and such a curve indicating the tonereproduction characteristics is determined for each primary color.

Various methods are known for determining an approximate function curvethat passes through such plurality of coordinate points that have beenplotted onto a two-dimensional coordinate system. For example, splinecurves and Bezier curves are widely known as approximate function curvesthat pass through a plurality of points, and if necessary, approximationusing such curves is performed.

As mentioned above, in the case of a general CRT monitor, upon plottingfive points O, Q1, Q2, Q3, and P as shown in FIG. 10, an approximationby a function curve defined by a power form is possible. However,measurements by the present inventor have shown that with a liquidcrystal display, a sigmoid (S-shaped) characteristics curve, such asthat shown in FIG. 11, is obtained in not so few cases. Though such asigmoid characteristics curve cannot be approximated by a general gammacharacteristics curve that is defined by a power form, approximationusing spline curves or Bezier curves, etc., can be performed.

However for practical use, approximation using spline curves or Beziercurves, etc., is not necessarily appropriate. This is because splinecurves and Bezier curves are curves for expressing contour shapes ofobjects used in drawing type plotting software and have properties thatare not suitable for expressing curves with physical significance.Specifically, the tone value and luminance, which are variables of thefunction that indicates tone reproduction characteristics, are bothvariables that should take on positive values and do not take onnegative values. The graph of FIG. 11 is thus a graph that is definedonly in the first quadrant of the two-dimensional coordinate system.However, when approximation by spline curves or Bezier curves, etc., isperformed, since an approximation that ignores such physicalsignificance is carried out, the resulting curve may run over into thesecond quadrant or the fourth quadrant.

Appropriate considerations are thus required in determining theapproximate curve.

The present inventor thus found that when for five points O, Q1, Q2, Q3,and P, plotted on the two-dimensional coordinate system, anapproximation by a function curve defined by a power form is attemptedand the approximation fails, it is effective to consider that the curveis a sigmoid characteristics curve, such as shown in FIG. 11, and todivide the curve into two portions by the method described below andapproximate each portion by a function curve defined by a power form.Specifically, for the example shown in FIG. 11, approximation by twofunction curves, that is a first function curve, passing through therespective points O, Q1, and Q2, and a second function curve, passingthrough the respective points Q2, Q3, and P, is carried out. Here, bothof the two function curves may be approximated by function curvesdefined by a power form. Curves that lie within the first quadrant willthus always be obtained.

This method is thus one wherein, when the five points plotted on thetwo-dimensional coordinate system are referred to as the first point tothe fifth point in the order of increasing coordinate value along thefirst coordinate axis, the first function curve, which passes throughthe first, second, and third points and is of the form wherein theluminance is expressed as a power of the tone value, and the secondfunction curve, which passes through the third, fourth, and fifth pointsand is of the form wherein the luminance is expressed as a power of thetone value, are determined by computation, and the curve formed byconnecting the first function curve and the second function curve isdeemed to be the curve indicating the tone reproduction characteristics.Though in such a case where two function curves are connected, there isthe possibility that the curvatures of the function curves arediscrepant at the third point that is to be the connection point (pointQ2 in FIG. 11), this will not present a problem in particular in usingthe resulting curve as a curve that indicates the tone reproductioncharacteristics.

<<<Section 5. More Preferable Test Patterns>>>

Test patterns, which are more preferable in putting the presentinvention into practice, will now be described. With the embodimentsdescribed up until now, a test pattern, made up of a square firstattribute region 10 and a frame-like second attribute region 20 thatsurrounds the periphery of the first attribute region as shown in FIG.3A, is used, and a reference pattern that is a stripe pattern, as shownin FIG. 3B, is formed inside second attribute region 20. Though such atest pattern is a pattern that has been used conventionally, it is notnecessarily an optimal test pattern.

The present inventor has found that more accurate measurements areenabled by using a test pattern, such as shown in FIG. 12A, in place ofthe conventional test pattern shown in FIG. 3A, and using a referencepattern, such as shown in FIG. 12B, in place of the conventionalreference pattern shown in FIG. 3B. Though the test pattern shown inFIG. 12A is made up of first attribute regions 50 for displaying an evenpattern and a second attribute region 60 for displaying a referencepattern, as shown by the enlarged plan view of FIG. 12B, the referencepattern is a pattern of a checkerboard design formed by firstsub-regions 61 (black cells in the FIGURE) and second sub-regions 62(white cells in the FIGURE). Though in FIG. 12A, hatching by means ofhorizontal lines is applied inside second attribute region 60 for thesake of illustration, in actuality, a reference pattern, which is acheckerboard pattern and having a reference luminance of 50%, as shownin the enlarged plan view of FIG. 12B, is formed inside second attributeregion 60. The characteristics of the test pattern shown in FIG. 12A andthe reference pattern shown in FIG. 12B and the unique effects obtainedby these characteristics will now be described.

(1) A Characteristic Concerning the Reference Pattern

A comparison of the reference pattern shown in FIG. 12B with thereference pattern shown in FIG. 3B shows that whereas the latter isarranged as a black-and-white stripe pattern, the former is arranged asa black-and-white checkerboard pattern. Here, the reference patternshown in FIG. 12B is a checkerboard pattern because this referencepattern happens to be a pattern that indicates a reference luminance of50%, and an essential point is that first sub-regions 61 (black) andsecond sub-regions 62 (white) are arranged as unit cells of the sameshape and size and the reference pattern is arranged from atwo-dimensional array of these unit cells. In particular, with theexample shown here, a reference pattern is arranged by arrayingrectangular (square in the present example) unit cells in the form of atwo-dimensional array.

In comparison to a reference pattern formed as a stripe pattern, areference pattern arranged from a two-dimensional array of unit cellshaving the same shape and size provides the effect of increasing thesimulated uniformity upon observation. During visual measurement by theoperator, a reference pattern will be observed from some viewingdistance, and the design itself will actually not be recognized directlyby the operator regardless of whether the pattern is of a stripe designor of a checkerboard design, and in both cases, the pattern will berecognized as a substantially gray, even pattern. However, since thecheckerboard design pattern is formed of finer unit cells, theuniformity during observation will be improved.

This characteristic is especially significant when a reference patternhaving a reference luminance besides 50% is formed. For example, in thecase of the embodiment described in Section 4, reference patterns of thethree reference luminance values of 25%, 50%, and 75% must be prepared,and the method of forming reference patterns from two-dimensional arraysof unit cells exhibits its effect especially in such a case. Examples inwhich reference patterns of a reference luminance of 25% and of 75% areformed using reference patterns in which rectangular unit cells arearrayed in two-dimensional arrays are shown in FIGS. 13A and 13B. InFIG. 13B, though the boundary lines of the respective unit cells makingup second sub-regions 62 (white) are drawn for the sake of description,in actuality, these boundary lines between white cells are notdisplayed.

The setting of the reference luminance is accomplished by changing thearea ratio of first sub-regions 61 (black) and second sub-regions 62(white). That is, in order to set the reference luminance to 25%, thearea ratio must be set to 3:1, and in order to set the referenceluminance to 75%, the area ratio must be set to 1:3. When referencepatterns, in which rectangular unit cells are arrayed in atwo-dimensional array, are used, the area ratios of 1:1 (FIG. 12B), 3:1(FIG. 13A), and 1:3 (FIG. 13B) can be set rationally while providingpatterns with which the simulated uniformity is secured adequately.

With all of these three reference patterns, a single cell group isformed from four cells, positioned in two rows and two columns. Here,when of the four unit cells making up each cell group, first sub-regions61 (black) are arranged from a pair of diagonally adjacent unit cellsand second sub-regions 62 (white) are arranged from the remaining pairof unit cells, the reference pattern with an area ratio of 1:1, which isshown in FIG. 12B, can be arranged. Also, when of the four unit cellsmaking up each cell group, a sub-region of one type is arranged from oneunit cell and sub-regions of the other type are arranged from theremaining three unit cells to form a reference pattern with an arearatio of 3:1 or 1:3, the reference pattern shown in FIG. 13A or 13B canbe arranged. In all cases, since the reference pattern that is formedwill be a repeated pattern of cell groups, each made up of four unitcells positioned in two rows and two columns, the simulated uniformitycan be secured adequately.

To summarize, by defining cell groups, each formed of four unit cells,which, using arbitrary odd numbers i and j, are referred to as the unitcell of the i-th row and j-th column, the cell of the i-th row and(j+1)-th column, the cell of the (i+1)-th row and j-th column, and thecell of the (i+1)-th row and (j+1)-th column, and making the pattern ofpositioning of the first sub-regions and second sub-regions the same forall cell groups, the reference pattern that is formed will be a repeatedpattern of cell groups, each made up of four unit cells positioned intwo rows and two columns that enables the simulated uniformity to besecured.

Meanwhile, in order to set the reference luminance to 25% or 75% bymeans of a conventional stripe type reference pattern, such as shown inFIG. 3B, an alignment of rows, such as black, black, black, white orblack, white, white, white, must be formed, and lowering of thesimulated uniformity thus cannot be avoided.

(2) A Characteristic Concerning the Shape of the First Attribute Region

Next, a comparison of the shape of first attribute region 10 in the testpattern shown in FIG. 3A and the shape of first attribute region 50 inthe test pattern shown in FIG. 12A shows that whereas the former is asquare, the latter is a circle. The present inventor considers that theboundary line between the first attribute region and the secondattribute region in the test pattern should not be a straight line butshould be a curve, and that for practical use, it is preferable for thecontour of the first attribute region that makes up the test pattern tobe a circle or an ellipse. This is because when the boundary linebetween the two regions is made a straight line, a regular pattern willbe conspicuous near the pattern. When as shown in FIG. 3A, the shape offirst attribute region 10 is made a square, a regular pattern will bevisually recognized along the contour of this square shape and this willhave an adverse effect on the matching judgment process. In particular,since not only the judgment of brightness matching but the judgment ofcolor matching must also be made in this invention, elements that havean adverse effect on the matching judgment process must be eliminated asmuch as possible.

(3) A Characteristic of Dispersedly Positioning the First AttributeRegions in Plural Locations

A major characteristic of the test pattern shown in FIG. 12A is thatfirst attribute regions 50 are positioned dispersedly at a plurality oflocations, and second attribute region 60 is arranged as a backgroundportion thereof. That is, whereas with the conventional test patternshown in FIG. 3A, just one first attribute region 10, formed as asquare, is positioned at the center, with the test pattern of thepresent invention shown in FIG. 12A, a plurality of first attributeregions 50, formed as circles, are positioned dispersedly horizontallyand vertically at a prescribed pitch.

A reason for dispersedly positioning first attribute regions 50 atplural locations in this manner is to make the total length of theboundary lines between first attribute regions 50 and second attributeregion 60 as long as possible. In measurements based on the basicprinciples of this invention, the task of comparing the brightness andcolor of the even pattern formed inside each first attribute region andthe reference pattern displayed inside the second attribute region isessential, and this comparison task can be performed more readily thelonger the boundary lines between the two types of regions. Actually inthe visual confirmation task performed by the operator, matching iscertified when first attribute regions 50 appear to have becomedissolved inside second attribute region 60 and the boundaries betweenthe two cannot be recognized. Thus in terms of carrying out matchingrecognition of higher precision, the longer the boundary lines betweenthe two types of regions, the more preferable.

By dispersedly positioning first attribute regions 50 at plurallocations, the total length of the boundary lines can be madecorrespondingly longer. Actually, from a comparison of the total lengthof the boundary lines of the test pattern shown in FIG. 3A with that ofthe test pattern shown in FIG. 12A, it should be readily understood thatthe latter is far longer. In opposition to the embodiment illustratedhere, the second attribute region may be positioned dispersedly atplural locations and the first attribute region may be made thebackground thereof instead (by making region 60 be of the firstattribute and regions 50 be of the second attribute in FIG. 12A).

For practical use, the total area of first attribute regions 50 and thetotal area of second attribute region 60 are preferably set equal toeach other. For example, in the case of the test pattern shown in FIG.12A, first attribute regions 50 are made up of a total of twelvecircular regions and second attribute region 60 is made up of thebackground region in which these circular regions are positioned, and inthis case, the total area of the total of twelve circular regions ispreferably set to be equal to the area of the background region. This isdone in consideration of making the display regions of the even patternsand the display region of the reference pattern, which are both objectsof comparison, the same in area to enable comparison on an equal basis.If, in the case where the matching of both brightness and color are tobe recognized as in the present invention, the area of one type ofregion is greater, the visual sense will be drawn to the region oflarger area, and matching may be recognized erroneously even ifrecognition of matching is not attained in the strict sense. By makingthe two types of regions equal in total area, comparison on an equalbasis, with which such erroneous recognition is eliminated, is madepossible.

(4) A Characteristic Concerning the Positioning Pitch of the FirstAttribute Regions

As mentioned above, a major characteristic of the test pattern of thepresent invention shown in FIG. 12A is that the first attribute (orsecond attribute) regions are positioned dispersedly at plurallocations. A characteristic concerning the pitch of this positioningwill now be described.

As will be described in detail later, it is known that in cases ofvisually distinguishing differences in brightness and color, the humanrecognition sensitivity is dependent on the spatial frequency of theobject. Thus an object to be visually recognized is preferablypositioned at a prescribed spatial frequency for which the humanrecognition sensitivity is deemed to be high. Thus with the test patternshown in FIG. 12A, all of first attribute regions 50 are preferably maderegions of the same shape and size and are positioned dispersedly on atwo-dimensional plane at a prescribed pitch that provides a prescribedspatial frequency for which the human recognition sensitivity is deemedto be high.

FIG. 14 is a plan view showing an example wherein first attributeregions 70 are formed of circles of the same radius r and are positionedat a prescribed pitch on a two-dimensional plane. More specifically, aplurality of one-dimensional region arrays, in each of which a pluralityof first attribute regions 70 are positioned in the horizontal directionat a prescribed pitch Px, are positioned in the vertically direction ata prescribed pitch Py (where Py=(√{square root over ( )}3)/2·Px) and sothat the phase is shifted by half a pitch between mutually adjacentone-dimensional region arrays. Put in another way, this two-dimensionalplane is arranged to be filled by a plurality of unit regions, each ofwhich is the hexagonal unit region that is illustrated, and the centersof seven circles are positioned at the center and at the respective apexpositions of the hexagonal shape that makes up each unit region.

By such positioning, the pitch of a pair of circles that are adjacent inthe horizontal direction will always be the pitch Px, the pitch of apair of circles that are adjacent in the diagonally up or down directionwill also always will be the pitch Px, and a pair of circles positionedadjacently in the two-dimensional plane will thus always be positionedat the pitch Px. Thus by setting the pitch Px to a pitch correspondingto the prescribed spatial frequency for which the human recognitionsensitivity is deemed to be high, a test pattern of preferablerecognition sensitivity will be obtained.

When as mentioned above, the total area of the first attribute regions,formed as circles, is set equal to the area of the second attributeregion arranged as a background portion thereof, a fixed relationshipholds between radius r and pitch Px. That is, the condition, that in thehexagonal region, the area of the regions inside the respective circles(the gray regions in the FIGURE) be equal to the area of the regionsoutside the respective circles (the white regions in the FIGURE), isimposed, and under this condition, the following approximation isderived from a geometrical area calculation:(radius r of each circle)≈(pitch Px)×(⅜)

Next, consider a model wherein a pair of objects (circular firstattribute regions) 70 are positioned at the pitch Px as shown in FIG.15. Let θ be the viewing angle when this pair of objects 70 is observedfrom a viewing distance L. In general, the sensitivity of a visionsystem that is measured with sine wave and rectangular wave patterns ofvarious frequencies that are fixed in time and displayed spatially iscalled a spatial frequency characteristic modulation transfer functionor contrast discrimination sensitivity characteristic, and thesensitivity of the human vision system with respect to objects that arepositioned repeatedly at a prescribed pitch is considered to bedependent on the viewing angle θ. For example, a graph of thesensitivity characteristics of the human vision system, such as shown inFIG. 16, is shown in “Haruo Sakata and Haruo Isono: Spatial frequencycharacteristics of chromaticity (color difference discriminationthreshold) in color perception, Journal of Television Science, 1977,Vol. 31(1), pp. 29-35.” Here, the abscissa indicates the spatialfrequency (unit: cycle/deg) of the observed object in logarithmic scale,and the ordinate indicates the relative sensitivity value of the humanvision system of discriminating brightness differences and colordifferences in an object.

In consideration of the characteristics such as shown in FIG. 16, in apoint of view of the operator viewing the test pattern, measurementresults of higher precision can be anticipated, if regions of the sameattribute are dispersedly positioned to arrange the test pattern at aprescribed pitch so as to obtain a spatial frequency in which goodsensitivity is exhibited for both brightness difference discriminationcharacteristics and color difference discrimination characteristics.

The table shown in FIG. 17 is obtained by extraction of the respectiveoptimal values from the graph of FIG. 16. That is, from the graph ofFIG. 16, the optimal value for the brightness difference discriminationcharacteristics (the spatial frequency corresponding to the peak of thecurve indicated by the alternate long and short dash line) is determinedas 2.5 [cycle/deg], and the optimal value for the yellow/blue colordifference discrimination characteristics (the spatial frequencycorresponding to the peak of the curve indicated by the solid line) isdetermined as 0.4 [cycle/deg]. Also, as a compromise value of the twocharacteristics, a value, for example, of approximately 0.6 [cycle/deg]can be set. Actually according to the graph shown in FIG. 16, somedegree of sensitivity is obtained for both characteristics at a spatialfrequency of approximately 0.6, and by forming a test pattern with whichthe spatial frequency is set to the compromise value of 0.6, fairly goodrecognition sensitivity will be provided for performing brightnessmatching recognition and color matching recognition.

The spatial frequency (unit: cycle/deg) and the viewing angle (unit:deg/cycle) are in an inverse relationship, and the viewing anglescorresponding to the respective spatial frequencies, 2.5, 0.4, and 0.6in the table of FIG. 17 are 0.40, 2.50, and 1.67, respectively. Thismeans that by positioning first attribute regions 70 at a pitch Px suchthat the viewing angle θ shown in FIG. 15 will be 0.40 deg, 2.50 deg, or1.67 deg, a pattern of optimal brightness difference discriminationcharacteristics, a pattern of optimal yellow/blue color differencediscrimination characteristics, or a pattern that is a compromise forboth characteristics will be obtained.

Since the viewing angle θ and the pitch Px are related to each other viathe viewing distance L by:Px=2L·tan(θ/2)

even if the viewing angle θ is set, unless the viewing distance L isdetermined, the pitch Px cannot be determined. However, in the case of ageneral monitor, the viewing distance of the operator will be maintainedwithin a substantially fixed range. For example, according to the VDTWorking Guidelines of the National Personnel Authority of Japan issuedon Dec. 16, 2002, it is deemed that a viewing distance of no less than40 cm must be secured, and in an actual working environment, thoughthere may be slight differences depending on the size of the monitor,etc., it can be considered that viewing distance is substantiallyapproximately 40 cm. Thus for practical use, the viewing distance L isset to approximately 40 cm and a pitch Px, with which fairly goodrecognition sensitivity can be obtained for both the brightnessdifference discrimination characteristics and the color differencediscrimination characteristics, is set accordingly.

For example, when the viewing distance L is set to 40 cm, the pitchcorresponding to the viewing angle θ of 1.67 deg, which is thecompromise value shown in FIG. 17 for both characteristics, will becalculated by the above equation as Px≈12 mm. Thus in the case of thetest pattern shown in FIG. 14, the setting, Px≈12 mm, is made. Also, inorder to make the total area of the first attribute regions that areformed as circles be equal to the area of the second attribute regionarranged as a background portion thereof, the radius of each circle iscalculated by the above equation, 37 r≈Px·⅜,” so that r≈4.5 mm. Thus inthe case of a monitor, wherein the size of a single pixel is 0.25 mm, atest pattern, wherein the radius of each circle is set to 18 pixels andthe pitch Px is set to 48 pixels, is displayed.

More strictly speaking, since as is indicated in the table of FIG. 17,the optimal value for brightness difference discriminationcharacteristics and the optimal value for color differencediscrimination characteristics differ, in a more preferable embodiment,a first pitch, enabling the obtaining of a spatial frequency thatindicates good sensitivity concerning brightness differencediscrimination characteristics for the operator who views the testpattern, and a second pitch, enabling the obtaining of a spatialfrequency that indicates good sensitivity concerning color differencediscrimination characteristics, are set respectively, and a process ofswitching the arrangement of the test pattern to be displayed isperformed so that a test pattern, in which regions of the same attributeare positioned dispersedly at the first pitch, is displayed when thebrightness matching recognition work is performed by the operator, and atest pattern, in which regions of the same attribute are positioneddispersedly at the second pitch, is displayed when the color matchingrecognition work is performed by the operator.

For example, with the table of FIG. 17, when the viewing distance L isset to 40 cm, the pitch and circle radius corresponding to a viewingangle θ of 0.40 deg, which is the optimal value for the brightnessdifference discrimination characteristics will be such that the pitchPx≈2.8 mm and the radius r≈1.1 mm. Meanwhile, the pitch and circleradius corresponding to a viewing angle θ of 2.50 deg, which is theoptimal value for the yellow/blue color difference discriminationcharacteristics will be such that the pitch Px≈17.5 mm and the radiusr≈6.6 mm. Thus in the case of performing the processes based on theflowchart shown in FIG. 9, a test pattern, with which circles arepositioned so that the pitch Px≈2.8 mm and the radius r≈1.1 mm, isdisplayed when performing the “brightness matching” recognition processof steps S2 and S3, and a test pattern, with which circles arepositioned so that the pitch Px≈17.5 mm and the radius r≈6.6 mm, isdisplayed when performing the “color matching” recognition process ofsteps S4 and S5.

The task of carrying out brightness or color matching recognition usinga test pattern in which a plurality of circles of the above-mentionedsizes are positioned will actually be felt by the operator not to be a“task of matching the brightness and color of the two types of regions”but to be a “task of adjusting so that there will be no non-uniformityof brightness and color in the test pattern as a whole.” That is, if thebrightness and color are not matched, it will be felt as if there is anon-uniformity of brightness or color at the cycle of the pitch Px.Visual measurements using the conventional test pattern shown in FIG. 3Aand visual measurements using this invention's test pattern shown inFIG. 12A will thus differ greatly in terms of the sensation of theoperator, and measurements using the test pattern of this invention willenable better results to be obtained.

<<<Section 6. Arrangement of a Tone Reproduction CharacteristicsMeasuring Device by this Invention>>>

The basic arrangement of a tone reproduction characteristics measuringdevice for color monitor by this invention will now be described withreference to the block diagram of FIG. 18. As illustrated, the tonereproduction characteristics measuring device for color monitoraccording to the present invention has a tone value designating means210, a reference pattern producing means 220, a pattern display means230, a tone value varying means 240, a coincidence signal input means250, and a characteristics computing means 260 as the main componentsand has a function of measuring the tone reproduction characteristics ofcolor monitor 100 by means of visual measurement operations performed bythe operator.

Since the measuring device of the invention can actually be realized byinstalling a prescribed program in personal computer 200 connected tocolor monitor 100 as shown in FIG. 1, the above components are actuallyrealized by the program installed in personal computer 200.

Tone value designating means 210 has a function of designatingcombinations of the tone values of the three primary colors, R, G, andB, for displaying the even pattern of uniform brightness and colorinside first attribute region 50 and designates the respective tonevalues of R, G, and B to pattern display means 230. Meanwhile, referencepattern producing means 220 has a function of generating a referencepattern having a prescribed reference luminance by making firstsub-regions, wherein the three primary colors, R, G, and B, respectivelytake on the minimum tone values, and second sub-regions, wherein thethree primary colors, R, G, and B, respectively take on the maximum tonevalues, exist in mixed manner at a prescribed area ratio inside secondattribute region 60. In the case of the embodiment described in Section5, the three types of reference pattern, shown in FIGS. 12B, 13A, and13B, can be generated selectively in accordance with the referenceluminance required for measurement.

Based on the data provided from these components, pattern display means230 displays a test pattern, such as that illustrated, on the screen ofcolor monitor 100. This pattern is a pattern made up of first attributeregions 50 and second attribute region 60 which are positioned tocontact each other, and in particular, the test pattern shown here isthe same as the test pattern shown in FIG. 12A. That is, first attributeregions 50 of circular shape are positioned at a prescribed pitch on atwo-dimensional plane, and second attribute region 60 is made up of thebackground portion. As mentioned above, the even patterns, based on thecombinations of the tone values of R, G, and B that were designated bytone value designating means 210, are displayed inside first attributeregions 50, and the reference pattern, produced by reference patternproducing means 220, is displayed inside second attribute region 60. Inactuality, prescribed electrical signals for making such a test patternbe displayed is provided from pattern display means 230 to color monitor100.

Tone value varying means 240 has a function of executing the varyingoperation of varying the respective tone values designated by tone valuedesignating means 210. By this varying operation, the brightness andcolor of the even pattern displayed inside first attribute region 50 arechanged. As mentioned in Section 2, the operations of varying the tonevalues include the brightness varying operation and the color varyingoperation. With the embodiment described in Section 2, tone valuevarying means 240 performs the brightness varying operation and thecolor varying operation in accordance with operation inputs from theoperator. In this case, tone value varying means 240 makes an operationpanel, such as shown in FIG. 6 or 7, be displayed on the screen of colormonitor 100 (normally to a side of the test pattern) and performs theprocess of varying the respective tone values designated by the tonevalue designating means 210 so that the brightness and color changebased on mouse operations, etc., performed by the operator. Meanwhile,in the case of the embodiment in which the varying operations areexecuted automatically as described in Section 3, the brightness varyingoperation and the color varying operation are executed according to theprocedures based on the flowchart of FIG. 9 and without waiting foroperation inputs form the operator.

Coincidence signal input means 250, in the state where varying operationis performed by tone value varying means 240, has a function ofinputting the coincidence signal, indicating the recognition that firstattribute regions 50 and second attribute region 60 have become matchedboth in brightness and color, from the operator viewing the test patterndisplayed on the screen of color monitor 100. In the case of anembodiment wherein the matching of brightness and the matching of colorare input separately of each other, coincidence signal input means 250comprises a brightness coincidence signal input means 251 and a colorcoincidence signal input means 252. For example, match button 30, shownin FIGS. 6 and 7 is a button that indicates the matching of bothbrightness and color, and by the operation of clicking this match button30, the input of the coincidence signal that indicates the matching ofboth brightness and color is performed. Meanwhile, brightness matchbutton 41, shown in FIG. 8, functions as brightness coincidence signalinput means 251 that indicates the matching of brightness, and colormatch button 42, shown in FIG. 8, functions as color coincidence signalinput means 252 that indicates the matching of color.

Characteristics computing means 260 recognizes the combinations of therespective tone values of R, G, and B, which are designated by tonevalue designating means 210 at the point at which the coincidence signalindicating the matching of both brightness and color is input fromcoincidence signal input means 250, to be the corresponding tone valuesof the respective primary colors that correspond to the referenceluminance value that is in accordance with the area ratio of the firstsub-regions and the second sub-regions that make up the referencepattern generated by reference pattern generating means 220, and basedon the reference luminance value and the corresponding tone values thatcorrespond to each other, executes a process of determining, bycomputation, curves that indicate the tone reproduction characteristicsaccording to the respective primary colors. The specific computationmethods are as have been described above. A graph that indicates thetone reproduction characteristics according to the respective primarycolors, R, G, and B is thus output. Though for the sake of description,the tone reproduction characteristics are shown in the form of a graphthat shows continuous functional relationships, the tone reproductioncharacteristics determined by characteristics computing means 260 do notneed take on the form of a graph and may instead take on the form, forexample, of a numerical table that indicates the correspondence betweenthe tone values and luminance values.

Thus by the above-described tone reproduction characteristics measuringdevice for color monitor, tone reproduction characteristics can bedetermined by visual recognition at high precision.

<<<Section 7. Method for Measuring Tone Reproduction CharacteristicsUsing a Sample Image>>>

A method for measuring tone reproduction characteristics by an approachthat differs from that of the embodiments described above will now bedescribed. The measuring method to be described in this Section 7 isbased on the basic principle of visually comparing a sample image outputon a physical medium, such as paper, and a sample image displayed on amonitor, and modifying provisional tone reproduction characteristicsbased on the comparison result to determine formal tone reproductioncharacteristics.

Here, an example of making a measurement using three sample images, Ha,Hb, and Hc, such as shown in FIG. 19, will be described. Though in theillustrated example, sample image Ha is a picture of a glass, sampleimage Hb is a picture of a sphere, and sample image Hc is a picture of acylinder, the contents of the picture may be anything. However, theindividual sample images are pictures that differ from each other inoverall brightness. That is, sample image Ha is a picture that is brightoverall, sample image Hb is a picture of intermediate brightnessoverall, and sample image Hc is a picture that is dark overall. Onecharacteristic of this embodiment is that a plurality of sample imagesthat differ from each other in overall brightness are prepared. Thoughthe number of sample images prepared is 3 in the example of FIG. 19, alarger number of sample images may be prepared.

The sample images Ha, Hb, and Hc shown in FIG. 19 are actually preparedin the form of image data. To be more specific, each sample image isformed of a set of plurality of pixels, and for example in the case ofan 8-bit color image, pixel values in the range of 0 to 255 are definedfor each of the three primary colors, R, G, and B in each individualpixel. Moreover, since as mentioned above, sample image Ha is a picturethat is bright overall, the pixel values of the majority of pixelsthereof are comparatively large, since sample image Hb is a picture ofintermediate brightness overall, the pixel values of the majority ofpixels thereof are of substantially intermediate values, and sincesample image Hc is a picture that is dark overall, the pixel values ofthe majority of pixels thereof are comparatively small.

Here, the mode value or the average value of the pixel values of allcolors of the individual pixels making up a single sample image will bedefined as the representative tone value of the sample image. To bespecific, suppose the representative tone value of sample image Ha shownin FIG. 19 is 197, the representative tone value of sample image Hb is130, and representative tone value of sample image Hc is 45 here. When aplurality of sample images that differ from each other in overallbrightness are prepared, the representative tone values of therespective sample images will be distributed discretely within the rangeof 0 to 255.

Three curves Cr, Cg, and Cb, such as shown in FIG. 20, are then preparedas curves indicating tone reproduction characteristics (gammacharacteristics). These three curves Cr, Cg, and Cb indicaterelationships between the input signal tone values and the actuallydisplayed luminance for the three primary colors, R, G, and B,respectively and, as mentioned above, are generally called “gammacurves.” An object of the measuring device of the present invention isto determine unique gamma curves for each individual color monitor, andin the case of the measuring device of the above-described embodimentshown in FIG. 18, curves, indicating the tone reproductioncharacteristics that are sought for, in other words, gamma curves areoutput from characteristics computing means 260.

By installing the gamma curves unique to each individual monitor asprofile data for the monitors, corrections based on these profile dataare enabled and universal display results that are not affected by theunique tone reproduction characteristics of the individual monitors canbe obtained.

The basic concept of the embodiment described in this Section 7 is toprovide arbitrary gamma curves as provisional tone reproductioncharacteristics to a personal computer, make sample images be displayedon the monitor screen upon carrying out corrections based on these gammacurves, and then performing operations of modifying the gamma curves sothat the brightness and colors of the sample images displayed on themonitor approach the brightness and colors of sample images output on aphysical medium and thereby modify the provisional tone reproductioncharacteristics to formal tone reproduction characteristics.

For example, the modifying operation using sample image Ha, shown inFIG. 19, can be performed as follows. First, arbitrary gamma curves Cr,Cg, and Cb, such as shown in FIG. 20, are prepared as the provisionaltone reproduction characteristics. This sample image Ha is thendisplayed on color monitor 100. A state wherein the sample image Ha isdisplayed on color monitor 100 is shown in FIG. 21. That is, sampleimage 510 a, which is shown in the FIGURE, is the sample image Ha thatis displayed on a display screen 500 a of the monitor.

Meanwhile, a physical output medium 520 a is a medium that is obtainedby outputting the sample image Ha on paper or other physical medium, andsample image 530 a is an image that is fixed on this physical medium.Generally, physical output medium 520 a can be obtained by providingimage data, corresponding to the sample image Ha, to a color printer andprinting the image onto a paper surface. However, in the case of theabove example, since the sample image Ha is arranged from image dataexpressed in the RGB system, conversion of the image data to the CMYsystem is carried out in the process of printing by the color printer.

As shown in FIG. 21, the operator can visually compare sample image 510a, which is displayed on display screen 500 a of the monitor, and sampleimage 530 a, which has been printed out on physical output medium 520 a.Though both are images displayed based on the image data of the originalsample image Ha, whereas sample image 510 a is an image obtained byapplying corrections based on provisional tone reproductioncharacteristics, such as shown in FIG. 20, on the image data of theoriginal sample image Ha, sample image 530 a is an image obtained on apaper surface upon applying the data conversion from the RGB system tothe CMY system on the image data of the original sample image Ha.

At a lower right portion of display screen 500 a shown in FIG. 21 aredisplayed three slide bars 511 to 513. These slide bars 511 to 513function as operation means for providing instruction inputs foradjusting the brightness and color of sample image 510 a. The operatorinputs instructions for adjusting the brightness and color of sampleimage 510 a by operating these slide bars 511 to 513 and therebyperforms the adjusting operation of matching the brightness and color tothose of sample image 530 a.

Slide bar 511 has a function of adjusting the brightness of sample image510 a, and by moving its knob to the left using a mouse, the image canbe made brighter, and by moving the knob to the right, the image can bemade darker. Adjustment of the brightness can also be performed byclicking the buttons provided at the respective ends of the bar. Forexample, when the “Bright” button is clicked, the knob moves by just aprescribed amount to the left, and when the “Dark” button is clicked,the knob moves by just a prescribed amount to the right.

Slide bar 512 has a function of adjusting a first tint (yellow/blue) ofsample image 510 a, and by moving its knob to the left using the mouse,the yellow component of the colors of the image can be made stronger,and by moving the knob to the right, the blue component of the colors ofthe image can be made stronger. Since yellow and blue are in acomplementary relationship, when one is made stronger, the other is madeweaker. Adjustment of the first tint can also be performed by clickingthe buttons provided at the respective ends of the bar. For example,when the “Yellow” button is clicked, the knob moves by just a prescribedamount to the left, and when the “Blue” button is clicked, the knobmoves by just a prescribed amount to the right.

Slide bar 513 has a function of adjusting a second tint (red/green) ofsample image 510 a, and by moving its knob to the left using the mouse,the red component of the colors of the image can be made stronger, andby moving the knob to the right, the green component of the colors ofthe image can be made stronger. Since red and green are in acomplementary relationship, when one is made stronger, the other is madeweaker. Adjustment of the second tint can also be performed by clickingthe buttons provided at the respective ends of the bar. For example,when the “Red” button is clicked, the knob moves by just a prescribedamount to the left, and when the “Green” button is clicked, the knobmoves by just a prescribed amount to the right.

Here, the brightness and colors of sample image 510 a are changed by theadjustment operations using the respective slide bars 511 to 513 notbecause modifications are made directly on the image data of theoriginal sample image Ha but because modifications are made on the gammacurves Cr, Cg, and Cb that indicate the provisional tone reproductioncharacteristics as shown in FIG. 20. Moreover, in the case of theembodiment illustrated here, modifications stressed on “portionscorresponding to the brightness of sample image Ha” are performed.

The principles of this modification process will now be described morespecifically using the gamma curves Cr, Cg, and Cb shown in FIG. 20 asexamples. As mentioned above, sample image Ha is a comparatively brightpicture and the representative tone value takes on a comparatively largevalue of 197. Thus in the adjustment operation using this sample imageHa, modifications stressed on portions of the gamma curves Cr, Cg, andCb corresponding to comparatively high brightness are made.Specifically, on the respective gamma curves Cr, Cg, and Cb, shown inFIG. 20, points Q7, Q8, and Q9, which take on the representative tonevalue of 197 of sample image Ha, are recognized as control points on therespective gamma curves, and after moving these control points inprescribed directions in accordance with instruction inputs (operationinputs concerning slide bars 511, 512, and 513) by the operator,modifications are made by smoothly deforming the gamma curves so thatthe curves pass through the control points after movement.

Which of the three gamma curves Cr, Cg, and Cb shown in FIG. 20 shouldbe subject to the modification and in which direction and how much thecontrol point should be moved are determined in accordance with theinstruction inputs of the operator. For example, consider themodification to be made in the case where slide bar 512, shown in FIG.21, is slid to the right and an instruction input in the direction of“weakening yellow” is provided. In this case, the color subject tomodification is blue. This is because yellow is the complement of blueand “weakening yellow” is equivalent “strengthening blue.” The gammacurve Cb for blue will thus be the curve subject to modification and thepoint Q9, which takes on the representative tone value of 197 on thiscurve Cb, will be the control point subject to movement.

Here, since the operator's instruction input indicates modification inthe direction of “strengthening blue,” the control point Q9 is moved tothe position of a point Q91 to the right, or moved to the position of apoint Q92 below, or moved to the position of a point Q93 positioneddiagonally to the lower right, and the gamma curve Cb is then modifiedsmoothly so as to pass through the control point after this movement.When modification is made by moving the control point Q9 to any of thepoints Q91, Q92, and Q93, the luminance values close to the tone valueof 197 of the gamma curve Cb after modification will decrease. As aresult, the luminance of blue in sample image 510 a, which is displayedon the monitor, will increase and blue will be strengthened. This isbecause, due to the lowering of the luminance values close to the tonevalue of 197 of the gamma curve Cb, which was provided as theprovisional tone reproduction characteristics concerning blue, acorrection of displaying blue more strongly is performed in order toperform color expression correctly on monitor 100 with such a gammacurve Cb.

In other words, that the operator provides an input, which instructsmodification in the direction of “strengthening blue,” means that theluminance values of the monitor's true gamma curve Cb for blue are lowerthan the luminance values of the current provisional gamma curve Cbshown in FIG. 20. That is, since the luminance values of the true gammacurve Cb for blue are lower than the luminance values of the provisionalgamma curve, the blue of the sample image Ha that was displayed on themonitor was weak in blue and the operator thus provided an instructioninput in the direction of “strengthening blue.” Thus in this case, amodification of lowering the luminance values of the current provisionalgamma curve Cb shown in FIG. 20 in the direction of approaching the truegamma curve Cb should be performed, and this can be done by moving, asmentioned above, the control point Q9 to the position of the point Q91to the right, or to the position of the point Q92 below, or to theposition of the point Q93 positioned diagonally to the lower right, andthen smoothly modifying the gamma curve Cb so that it passes through thecontrol point after this movement. The movement amount of the controlpoint Q9 is determined in accordance with the amount of sliding of slidebar 512.

Needless to say, since the modification of the gamma curve Cb isperformed so that the curve will be smooth as a whole, the positions ofthe other illustrated points Q6 and Q3 will also be modified slightly.However, the modification will mainly be stressed on the vicinity of thetone value of 197. Since various methods are known for modifying theentirety of a curve upon moving a specific control point defined on asmooth curve, a detailed description of such a method will be omittedhere.

In a case where the operator slides slide bar 512 to the left andthereby provides an instruction input in the direction of “strengtheningyellow (weakening blue),” modification is performed by moving thecontrol point Q9 to the left, upwards, or diagonally to the upper left.Also, in the case where an adjustment of sliding slide bar 513 isperformed, since red and green will be the subject of modification, thecontrol point Q7 or the control point Q8 is moved to performmodification of the gamma curve Cr or the gamma curve Cg. Since red andgreen are in a mutually complementary relationship, no matter in whichdirection slide bar 513 is slid, the modification can be made bymodifying just the gamma curve Cr, or by modifying just the gamma curveCg, or by modifying both curves.

Meanwhile, in a case where the operator slides slide bar 511 to providean instruction input of adjusting the brightness, equivalentmodifications are made on all three gamma curves Cr, Cg, and Cb. Forexample, when slide bar 511 is slid to the left to provide aninstruction input in the direction of “increasing the brightness,” allof the control points Q7, Q8, and Q9 are moved to the right, downwards,or diagonally to the lower right and all gamma curves Cr, Cg, and Cb aremodified accordingly. Since the luminance values of the gamma curvesthat indicated the provisional tone reproduction characteristics willthen be lowered, corrections in the direction of increasing theluminance will be performed in order to perform display correctly andconsequently, the display luminance will increase.

Though obviously in actuality, when a color adjustment is made usingslide bar 512 or 513, the brightness will change slightly as well, andoppositely when a brightness adjustment using slide bar 511 is made, thecolor will change slightly as well, as the brightness adjustment andcolor adjustment are repeated, the brightness and color of sample image510 a on the monitor will gradually approach the brightness and color ofsample image 530 a on physical output medium 520 a. And at the stage atwhich the operator recognizes that both are matched in brightness andcolor, he/she clicks match button 514. With the present embodiment, thegamma curves Cr, Cg, and Cb, at the point at which this match button isclicked (actually, at the point at which all match buttons 514 shown inFIGS. 21 to 23 have been clicked), are output as curves indicating theformal tone reproduction characteristics.

Consequently, by performing adjustment by the above-described procedure,since modifications that are in accordance with the operator'sinstruction inputs are applied to the arbitrary gamma curves Cr, Cg, andCb that were provided at the initial stage as provisional tonereproduction characteristics, the modified gamma curves Cr, Cg, and Cbat the point at which match button 514 is pressed will indicatepreferable tone reproduction characteristics from the standpoint ofmatching the brightness and color when sample images 510 a and 530 a areviewed.

When the modification tasks using sample image Ha are thus completed,modification tasks using sample image Hb are performed subsequently inthe same manner. The provisional tone reproduction characteristics thatare provided at the initial stage of the modification tasks are thegamma curves Cr, Cg, and Cb that were obtained at the point ofcompletion of the modification tasks performed using sample image Ha.FIG. 22 is a plan view showing the screen for the modification operationusing sample image Hb. A sample image 510 b is displayed on a displayscreen 500 b, and modification operations using slide bars 511, 512, and513 are performed by comparison with a sample image 530 b that has beenprinted out on a physical output medium 520 b. Since the representativetone value of sample image Hb is 130, with the modification operationshere, points Q4, Q5, and Q6 on the gamma curves Cr, Cg, and Cb, shown inFIG. 20, are used as control points to modify the respective curves bythe method of moving these control points and modifications stressed onportions of intermediate brightness are carried out.

Lastly, modification tasks using sample image Hc are performed in thesame manner. The provisional tone reproduction characteristics that areprovided at the initial stage of the modification tasks are the gammacurves Cr, Cg, and Cb that were obtained at the point of completion ofthe modification tasks performed using sample image Hb. FIG. 23 is aplan view showing the screen for the modification operation using sampleimage Hc. A sample image 510 c is displayed on a display screen 500 c,and modification operations using slide bars 511, 512, and 513 areperformed by comparison with a sample image 530 c that has been printedout on a physical output medium 520 c. Since the representative tonevalue of sample image Hc is 45, with the modification operations here,points Q1, Q2, and Q3 on the gamma curves Cr, Cg, and Cb, shown in FIG.20, are used as control points to modify the respective curves by themethod of moving these control points and modifications stressed on darkportions are carried out.

When all of the modification operations using the three sample imagesHa, Hb, and Hc have been completed, the tone reproductioncharacteristics measurement tasks concerning color monitor 100 iscompleted. Thus in regard to Cr, Cg, and Cb shown in FIG. 20,modification using the bright sample image Ha is performed in regard tocharacteristics in the vicinity of a tone value of 197, modificationusing sample image Hb of intermediate brightness is performed in regardto characteristics in the vicinity of a tone value of 130, andmodification using the dark sample image Hc is performed in regard tocharacteristics in the vicinity of a tone value of 45, and modificationusing respectively appropriate sample images for different portions ofthe gamma curves is thus completed.

Needless to say in actuality, there is a high likelihood that when,after performing the modification operations using the three sampleimages Ha, Hb, and Hc in that order, visual comparison of sample imageHa is carried out again, the state of matching of brightness and coloris found to have become disrupted. This is because, though, due to themovement of a control point, the modification of a gamma curve isstressed on the vicinity of the corresponding control point, thismodification affects the entirety of the gamma curve. Thus for practicaluse, the modification operations using the three sample images Ha, Hb,and Hc are preferably repeated a plurality of times in a cyclic mannerif necessary.

When, in the final stage, the operator recognizes that, for all of thethree sample images, the brightness and color of the images displayed onthe monitor match the brightness and color of the images output on thephysical output medium, the gamma curves Cr, Cg, and Cb at that pointare output as curves indicating the formal tone reproductioncharacteristics concerning color monitor 100. Needless to say, it isextremely difficult to make the brightness and color of images displayedon a monitor be matched completely with those of images output on aphysical output medium in a strict sense. First of all, unless the whiteon color monitor 100 is completely matched with the white on thephysical output medium, it is impossible to perform an adjustment ofmaking the two images be matched strictly in terms of brightness andcolor. Thus with the present embodiment, “matching of brightness andcolor” signifies that the degree of closeness of these aspects havereached a state where matching can be recognized under the sensoryjudgment based on visual recognition by the operator.

The gamma curves, Cr, Cg, and Cb, which are output as the formal tonereproduction characteristics by the above-described method for measuringtone reproduction characteristics using sample images do not indicatemonitor characteristics that are based on absolute standards but onlyindicate relative characteristics based on the sample images. Forexample, even if measurements using the image data of the same sampleimage Ha are performed on the same color monitors, if different printersor different papers are used in preparing the physical output medium,the gamma curves that are output as the formal tone reproductioncharacteristics will differ. This is because, as with monitors, printersalso have respectively unique tone reproduction characteristics, andoutput media that are printed using the same image data will differ inbrightness and color if different printers are used.

Thus in order to determine tone reproduction characteristics that arebased on the absolute standard for each individual color monitor by themethod described here, the brightness and color of the sample imagesused must be measured physically and some form of correction based onthe measurement results must be applied. However, for use in a practicalapplication of modifying the scattering of tone reproductioncharacteristics among a plurality of color monitors used in DTPprocesses, there is no need to determine tone reproductioncharacteristics based on the absolute standard. For example, consider anapplication in an environment where DTP processes are to be executed bydivision of labor among a staff of 50 and the tone reproductioncharacteristics of each of 50 color monitors are to be measured in orderto correct the scattering of the tone reproduction characteristics amongthe respective color monitors. In this case, 50 sheets of the physicaloutput media are prepared by printing out the same sample images onpaper of the same quality using the same printer. Since the sampleimages that are printed out on the 50 physical output media are the samein brightness and color, when the tone reproduction characteristics ofthe 50 color monitors are respectively measured using these 50 physicaloutput media, the measurement results that are obtained will all bebased on the same standards and the intended purpose will thus beachieved. Needless to say, a single physical output medium may be sharedfor measurement of the tone reproduction characteristics of the 50 colormonitors.

Though as the sample images, images of any picture may be used, in orderto facilitate the visual comparison work performed by the operator, itis preferable to use images that can be recognized as being achromaticpictures when viewed by the operator. Though obviously the actual imagesthat are displayed on the monitor are images that are displayed asmixtures of the three primary colors, R, G, and B, by using images thatcan be recognized, when observed by the naked eye, as pictures that areexpressed in shades of gray (images, for which the tone values of thethree primary colors R, G, and B of a single pixel are substantially thesame), the judgment of color matching can be performed especiallyreadily. This is because the sensitivity of perception of colorcomponents by human eyes is highest in the vicinity of the achromaticstate.

For example, if a bright red color is used as a base and the redness isstrengthened slightly or the redness is weakened slightly, such adelicate change of color cannot be sensed readily by the naked eye.However, if an achromatic color is used as a base and the redness isstrengthened slightly or the redness is weakened slightly (actually, thecomplementary color of green is strengthened slightly), such a change ofcolor can be sensed by the naked eye even if the change is delicate.When an achromatic color is used as a base, a lightly reddish state or alightly greenish state can be sensed readily by the naked eye.

<<<Section 8. Tone Reproduction Characteristics Measuring Device ThatUses Sample Images>>>

The arrangement and operations of a device for measuring tonereproduction characteristics of color monitors based on the principlesdescribed in Section 7 will now be described. FIG. 24 is a block diagramthat shows the basic arrangement of this device. As illustrated, thisdevice has a tone reproduction characteristics storage means 410, animage data storage means 420, an image display means 430, acharacteristics modifying means 440, a coincidence signal input means450, and a physical output media 520 as the major components, and has afunction of measuring the tone reproduction characteristics of colormonitor 100 based on visual measurement operations by the operator.

Of the respective components of this measuring device, the componentsbesides physical output media 520 are all components that can berealized by installing a prescribed program in personal computer 200connected to color monitor 100, and in actuality are realized by aprogram that is installed in personal computer 200.

Tone reproduction characteristics storage means 410 is a component forstoring provisional tone reproduction characteristics, and specificallyas shown in FIG. 20, is arranged by a storage device for storing datacorresponding to the gamma curves Cr, Cg, and Cb, which respectivelyindicate the relationships between tone value and luminance for thethree primary colors, R, G, and B, as shown in FIG. 20. The gamma curvesthat are stored here are provisional tone reproduction characteristicsconcerning color monitor 100, which is the object of measurement, andare modified gradually by the measurement tasks. In the final stage, thegamma curves stored here are output as the formal tone reproductioncharacteristics concerning color monitor 100.

Image data storage means 420 is a component that stores the image dataof sample images to be used for measurement and is arranged by a storagedevice for data storage. With the embodiment described here, the imagedata of the three sample images Ha, Hb, and Hc, shown in FIG. 19, areprepared inside image data storage means 420. In general, the image dataof a plurality (M) of sample images that differ in overall brightnessare prepared inside image data storage means 420.

Image display means 430 is a component that performs a process of makingthe sample images prepared inside image data storage means 420 bedisplayed on screen 500 of color monitor 100. This image display means430 has a function such that, when the tone reproduction characteristicsof color monitor 100 are assumed to be the provisional tone reproductioncharacteristics stored inside tone reproduction characteristics storagemeans 410, prescribed tone corrections are made on the image data storedinside image data storage means 420 so that a sample image will bedisplayed on color monitor 100 with correct tone reproductionproperties, and the image data after correction are provided to colormonitor 100. A sample image 510 that is displayed on screen 500 is thusan image to which tone corrections, based on the provisional tonereproduction characteristics that are stored inside tone reproductioncharacteristics storage means 410 at that point, are applied.

Meanwhile, each physical output medium 520 is a component obtained byoutputting a sample image onto a paper surface or other physical mediumbased on image data stored inside image data storage means 420 and has asample image 530 printed on its surface. If M sample images are preparedinside image data storage means 420, M physical output media thatrespectively correspond to these M sample images are prepared. With theembodiment described here, since image data on the three sample imagesHa, Hb, and Hc are prepared inside image data storage means 420, thethree physical output media 520 a, 520 b, and 520 c are prepared asshown in FIGS. 21 to 23.

The operator visually compares a sample image 510 on screen 500 with asample image 530 on a physical output medium 520, and for this process,the sizes of the images are preferably set to be substantially the same.This is because when the brightness and color of two images are comparedby the naked eyes, a more accurate comparison is enabled when the imagesare of substantially the same size. Thus in preparing a physical outputmedium 520 using a printer, it is preferable to make arrangements sothat a sample image 530 of substantially the same size as sample image510 on screen 500 will be printed.

Characteristics modifying means 440 has a function of receiving, fromthe operator who visually compares sample image 510, displayed on screen500 of the color monitor, and sample image 530, displayed on physicaloutput medium 520, instruction inputs in the direction of making theimages become matched in brightness and color, and modifying theprovisional tone reproduction characteristics stored in tonereproduction characteristics storage means 410 based on the instructioninputs.

With the embodiment described in Section 7, the modification operationsby characteristics modifying means 440 are performed in a manner whereinthe brightness modifying operation and the color modifying operation areperformed separately. The brightness modifying operation is theoperation of modifying the tone reproduction characteristics based on aninstruction input that instructs mainly the changing of the brightnessof sample image 510 displayed on screen 500 and, for example, isexecuted based on an instruction input that moves slide bar 511, shownin FIG. 21, to the left or right. Meanwhile, the color modifyingoperation is the operation of modifying the tone reproductioncharacteristics based on an instruction input that instructs mainly thechanging of the color of sample image 510 displayed on screen 500 and,for example, is executed based on an instruction input that moves slidebar 512 or 513, shown in FIG. 21, to the left or right. As described inSection 7, when the brightness modifying operation is performed, all ofthe respective gamma curves of the three primary colors, R, G, and Bthat are stored in tone reproduction characteristics storage means 410are modified, while when the color modification operation is performed,only the gamma curves of the colors subject to modification aremodified.

Also as described above, the modification of a gamma curve is stressedon portions corresponding to the brightness of the sample image that isused for visual comparison, and for example, when visual comparison ofsample image Ha of a bright picture is performed, modification isstressed mainly on the vicinity of the tone value of 197 shown in FIG.20.

In general, when an instruction input concerning an i-th sample imageamong a plurality (M) of sample images is received, modificationsstressed on “the portions corresponding to the brightness of the i-thsample image” are made on the provisional tone reproductioncharacteristics stored in tone reproduction characteristics storage mean410. In the case of the specific example described in Section 7, whencharacteristics modifying means 440 receives an instruction inputconcerning the i-th sample image, the point on a gamma curve with therepresentative tone value of the i-th sample image is recognized as thecontrol point and the modification of approaching the true tonereproduction characteristics is performed by moving the control point ina prescribed direction in accordance with the instruction input andthereafter modifying the gamma curve smoothly so that it passes throughthe control point after movement. Here, as the representative tone valueof the sample image, the mode value or the average value of the pixelvalues of all colors of the individual pixels indicated by the imagedata stored in image data storage means 420 is used.

Coincidence signal input means 450 is the component that inputs, fromthe operator the coincidence signal, which indicates the recognitionthat sample image 510 and sample image 530 are matched in brightness andcolor. Match buttons 514, shown in FIGS. 21 to 23, are buttons forindicating the recognition of matching in regard to a specific sampleimage, and coincidence signal input means 450 can be realized by acomponent that judges that the coincidence signal has been input fromthe operator when, for example, match button 514 has been clicked forall sample images. Or, a special button that indicates that the matchinghas been recognized for all sample images may be prepared separately.

Characteristics output means 460 outputs a graph, indicating theprovisional tone reproduction characteristics (the gamma curves Cr, Cg,and Cb) stored in tone reproduction characteristics storage means 410 atthe point at which the coincidence signal has been input from thecoincidence signal input means, as the formal tone reproductioncharacteristics of color monitor 100. The tone reproductioncharacteristics that have thus been output are the final measurementresults of the tone reproduction characteristics measuring deviceaccording to the present invention.

FIG. 25 is a flowchart showing the characteristic measurement processprocedures using the measuring device shown in FIG. 24. First, in stepS11, the image data of a plurality (M) of sample images that differ inoverall brightness are prepared. With the above-described example, M=3and the image data of three sample images Ha, Hb, and Hc are prepared.In step S12, which follows, a printer, etc., is used to output the Msample images onto physical media and M physical output media arethereby prepared. With the above-described example, the three physicalmedia 520 a, 520 b, and 520 c are prepared.

Next in step S13, the parameter i is set to the initial value of 1. Thisparameter i is a parameter for repeating the same procedure on each ofthe M sample images and is incremented by 1 each time in step S19 untili=M is reached in step S18.

In step S14, the process of displaying the i-th sample image on colormonitor 100 upon performing the tone corrections using the provisionaltone reproduction characteristics is performed. In the case of theabove-described example, when the parameter i=1, the first sample image510 a is displayed on screen 500 as shown in FIG. 21. The next step S15is a process operation performed by the operator, and the i-th sampleimage displayed on color monitor 100 and the i-th physical output mediumare compared visually. When the parameter i=1, sample image 510 a andsample image 530 a are compared as shown in FIG. 21.

In step S16, whether or not it is recognized that both the brightnessand color are matched as a result of comparison is judged, and ifmatching is not recognized, modifications are performed in step S17.That is, modifications stressed on the “portions corresponding to thebrightness of the i-th sample image” are performed according to theinstruction input of the operator on the provisional tone reproductioncharacteristics stored in tone reproduction characteristics storagemeans 410 at this point.

The respective procedures of steps S14, S15, S16, and S17 are thusrepeatedly executed until matching is recognized in step S16 (untilmatch button 514 is clicked). When matching is recognized in step S16,step S18 and step S19 are carried out to renew the parameter i and thenthe same processes are executed on the next sample image. When the sameprocesses have thus been completed for all of the M sample images, stepS20 is entered from step S18 and the process of outputting theprovisional tone reproduction characteristics, which are stored in tonereproduction characteristics storage means 410 at this point, as theformal tone reproduction characteristics is executed.

<<<Section 9. Modification Examples Using Representative LuminanceValues in Place of Representative Tone Values>>>

Lastly, modification examples of the embodiments described in Section 7and Section 8 will be described. With the embodiment described inSection 7, a representative tone value is defined for each sample image,and in the modification operations using a specific sample image,modifications stressed on the portions of the vicinity of therepresentative tone value of the sample image are performed on the gammacurves that indicate the tone reproduction characteristics. For example,since the representative tone value of sample image Ha, shown in FIG.19, is 197, modifications, using the points Q7, Q8, and Q9, which havethe tone value of 197 on the respective gamma curves as shown in FIG.20, as the control points, are carried out in the modificationoperations using sample image Ha.

With a modification example described here, a representative luminancevalue is defined for each sample image, and in modification operationsusing a single sample image, modifications stressed on the portions inthe vicinity of the representative luminance value of the sample imageare performed on the gamma curves that indicate the tone valuereproduction characteristics.

Since the tone values of a sample image are provided as the pixel valuesof the individual pixels that make up the image data of the sampleimage, the representative tone value can be determined uniquely as themode value or average value of these pixel values. On the other hand,the luminance value of a sample image are values that can be determinedonly after the sample image has been displayed on a monitor or output ona physical output medium. Thus even if the respective image data forthree sample images Ha, Hb, and Hc are prepared in image data storagemeans 420, the representative luminance values of the respective sampleimages Ha, Hb, and Hc cannot be determined directly from the image data.The present inventor considers the following two methods to be effectiveas methods for determining the representative luminance values of therespective sample images Ha, Hb, and Hc.

In a first method, a value, obtained by conversion by a prescribedconversion method based on the representative tone value, is used as therepresentative luminance value. Generally as shown in FIG. 20, therelationship between tone value and luminance value is not a linearrelationship and a unique curve is exhibited in accordance with themonitor or printer, etc. In the first place, this invention's tonereproduction characteristics measuring device is a device fordetermining such curves. However, the representative luminance valuethat is to be determined here does not need to be an accurate value.This is because the role of the representative tone value or therepresentative luminance value in this invention is to simply serve asan index for indicating which portions of the gamma curves indicatingthe tone reproduction characteristics should be stressed in carrying outmodifications, and exactness is thus not required.

Thus by defining a rough relationship, such as “the tone value and theluminance value are in a linear relationship,” the representativeluminance value can be converted uniquely from the representative tonevalue. FIG. 26 is a diagram showing an example of such conversionresults. Here, under the premise that the tone values take on a range of0 to 255, the luminance values take on a range of 0% to 100%, and theseare in a linear relationship, the simple conversion equation of:luminance value=tone value/255 is defined. As a result, therepresentative luminance value of sample image Ha is determined based onthe representative tone value 197 as being “197/255=78%,” therepresentative luminance value of sample image Hb is determined based onthe representative tone value 130 as being “130/255=51%,” and therepresentative luminance value of sample image Hc is determined based onthe representative tone value 45 as being “45/255=18%.” Though suchrepresentative luminance values determined by such conversion areobviously not accurate values, these are adequate for use as indicesindicating positions of the gamma curves to be stressed in makingmodifications.

Needless to say, more accurate conversions can be carried out. Forexample, in general, data files, called ICC profiles, which have beenestablished by the ICC (International Color Consortium), are used tocarry out color management between a personal computer and input/outputequipment. With many commercially available printers, ICC profiles areprovided by manufacturers and ICC profiles can also be prepared for anarbitrary printer by known measurement methods. Arbitrary RGB tonevalues can be converted to a luminance value using such an ICC profile.Thus by using the ICC profile of the specific printer that was used tooutput the physical media, more accurate conversion from therepresentative tone value to the representative luminance value isenabled.

A second method is to use a physical measuring device to actuallymeasure the average luminance of the entirety of the sample image on aphysical output medium and use the actually measured value as it is asthe representative luminance value of the sample image. Specifically,the representative luminance value for sample image Ha is determined byactual measurement of physical output medium 520 a, shown in FIG. 21,the representative luminance value for sample image Hb is determined byactual measurement of physical output medium 520 b, shown in FIG. 22,and the representative luminance value for sample image Hc is determinedby actual measurement of physical output medium 520 c, shown in FIG. 23.Though this method requires actual measurements by a physical method,accurate representative luminance values can be obtained.

When the representative luminance values have been obtained for therespective sample images, the control points are defined in accordancewith the representative luminance values, and the gamma curves aremodified accordingly. FIG. 27 is a graph for describing the concept ofmodifications stressed on portions in the vicinity of the representativeluminance values. When, as in the example of FIG. 26, the representativeluminance value of sample image Ha is determined as being 78%, therepresentative luminance value of sample image Hb is determined as being51%, and the representative luminance value of sample image Hc isdetermined as being 18%, modifications on the respective curves usingsample image Ha are performed by moving the control points Q1, Q2, andQ3, modifications on the respective curves using sample image Hb areperformed by moving the control points Q4, Q5, and Q6, and modificationson the respective curves using sample image Hc are performed by movingthe control points Q7, Q8, and Q9 as shown in FIG. 27.

<<<Section 10. Method of Automatically Varying the Tone ReproductionCharacteristics>>>

With the embodiments described in Section 7 to Section 9, examples,wherein instructions from the operator are input by operation of slidebars 511 to 513, such as shown in FIGS. 21 to 23 and the tone valuereproduction characteristics (gamma curves) are modified based on theseinstructions, were described. Here, a method of lightening the load ofsuch instruction inputs by the operator will be described.

The central aim of this method is the same as that of the embodimentdescribed in Section 3. That is, the shape of a gamma curve is variedautomatically with time in accordance with prescribed variationconditions that had been determined in advance, and the operator is madeto view a sample image on the screen of a color monitor and a sampleimage on a physical output medium and instruct the point at which thebrightness and color can be recognized to be matched most closely. Byrepeating the same process under various variation conditions, the shapeof the provisional gamma curve is made to approach the shape of the truegamma curve gradually. And at the stage at which approximation of somedegree is achieved, the operator is made to input the coincidence signalthat indicates the recognition that the images are matched in brightnessand color, and the provisional gamma curves at that point are output asthe formal gamma curves.

With the above-described embodiment, when, for example, a modificationoperation concerning the yellow/blue color is to be performed usingsample image Ha, shown in FIG. 19, the operator is made to adjust slidebar 512, shown in FIG. 21 to perform a modification of moving thecontrol point Q9 on the gamma curve Cb, shown in FIG. 20, in aprescribed direction. With the embodiment described here, the shape ofthe gamma curve Cb is varied with time by automatically and cyclicallyvarying the position of the control point Q9 in a prescribed direction.

For example, the control point Q9 shown in FIG. 20 is a point having atone value of 197, and when this tone value is varied within a rangeof±5, the tone value of the control point Q9 is varied within the rangeof 192 to 202. Consequently, the position of the control point Q9undergoes reciprocating motion to the left and right in FIG. 20.Obviously, when the position of the control point Q9 changes, the shapeof the gamma curve Cb is also varied smoothly so that it passes throughthe position of the new control point Q9. The gamma curve Cb is thusmodified repeatedly in a cyclic manner within a prescribed range basedon the shape shown in FIG. 20. By thus varying the gamma curve Cbcyclically, the yellow/blue color of sample image 510 a, shown in FIG.21, is varied cyclically and the same effect as the operations of movingslide bar 512 to the left and right in the above-described embodiment isprovided.

To summarize, the embodiment described here provides the same effect asmoving the slide bar, shown in FIG. 21, to the left and rightautomatically at the system side. Needless to say, slide bars 511 to513, such as shown in FIG. 21, do not need to be provided. The operatorviews sample images 510 a and 530 a and, at the point at which he/sherecognizes that the yellow/blue color of the images have become closestto each other, performs the instruction input indicating this by a mouseclick or other method. Since the gamma curve Cb at the point at whichthe operator performs the instruction input will be the most preferablegamma curve at that point, modification using this curve as the newgamma curve Cb is performed.

The gamma curves Cg and Cr are also modified by the same method. Thatis, here, the gamma curve Cg is varied cyclically by moving the controlpoint Q8 in a reciprocating manner to the left and right, the operatoris made to perform instruction input at the point at which he/sherecognizes that the red/green color of the images have become closest toeach other, and the gamma curve at that point is handled as the newgamma curve Cg. Likewise, the gamma curve Cr is varied cyclically bymoving the control point Q7 in a reciprocating manner to the left andright, the operator is made to perform instruction input at the point atwhich he/she recognizes that the red/green color of the images havebecome closest to each other, and the gamma curve at that point ishandled as the new gamma curve Cr.

Meanwhile for the recognition of brightness matching, the control pointsQ7 to Q9 are moved reciprocatingly to the left and right at the samephase to thereby vary the three gamma curves Cr, Cg, and Cbsimultaneously, the operator is made to perform instruction input at thepoint at which the images have become closest to each other inbrightness, and the respective gamma curves at that point are handled asthe new gamma curves Cr, Cg, and Cb.

Obviously when such a brightness modification process is executed, thecolor balance that had been adjusted may become disrupted, andoppositely when a color modification process is executed, the brightnessbalance may become disrupted. Thus for practical use, the adjustment ofcolor and the adjustment of brightness are executed in alternationrepeatedly and arrangements are made to gradually narrow the range ofvariation of the control point as in the embodiment described in Section3. The direction of variation of the control point may be a verticaldirection or an inclined direction.

When the modifications using sample image Ha shown in FIG. 19 arecompleted, the modification processes using sample image Hb areperformed. Here, the control points Q4, Q5, and Q6, shown in FIG. 20,are respectively varied within prescribed ranges and modifications ofmainly varying the central portions of the respective gamma curves Cr,Cg, and Cb are performed. Lastly, the modification processes usingsample image Hc are performed. Here, the control points Q1, Q2, and Q3,shown in FIG. 20, are respectively varied within prescribed ranges andmodifications of mainly varying the dark portions of the respectivegamma curves Cr, Cg, and Cb are performed. Obviously, a second round ofthe modification processes using sample image Ha may thereafter beexecuted.

When after performing such modification processes, the recognition, thatthe sample images are matched (or have become close to each other withina certain allowable range) in both brightness and color, is obtained asa result of visual comparison by the operator, the final coincidencesignal is made to be input. However, for practical use, a signal thattakes the form of a “final coincidence signal” does not need to be inputanew necessarily, and it suffices to handle the instruction input(instruction indicating that the color or brightness have become matchedmost closely), which is input lastly in the adjustment operationsconcerning sample image Hc, as the final coincidence signal.

Though an embodiment of automatically varying the tone reproductioncharacteristics has been described, in consideration of thecomputational capability of present computers, some measures are neededfor practical use in order to put the embodiment described in thisSection 10 into practice. With both the embodiment described in Section3 and the embodiment described in this Section 10, the color andbrightness of the displayed object on the screen appear to varygradually with time to the operator. However, in terms of the contentsof processing by the system, whereas in the case of the embodimentdescribed in Section 3, tone value varying means 240 (FIG. 18) needs tovary only the tone value inside tone value designating means 210directly and thus just a process of simply increasing or decreasing thedigital data needs to be performed, in the case of the embodimentdescribed in this Section 10, characteristics modifying means 440 (FIG.24) must perform the process of modifying a gamma curve stored in tonereproduction characteristics storage means 410. Moreover, since thecurve after modification must be a curve that passes through the controlpoint at a specific position, the computational load for determiningsuch a curve is considerably large.

Though in both the embodiment described in Section 3 and the embodimentdescribed in this Section 10, a cyclically varying image must bedisplayed to the operator, a display cycle that is too long will be poorin terms of practical use. For example, a form of operation, wherein,while displaying an image that varies in a cycle of 10 seconds, thepoint at which compared images become closest to each other is to beinstructed by an operator, is sufficiently practical. However, if thecycle of variation becomes of the order of 10 minutes, it becomesdifficult for the operator to maintain his/her attention and this isthus poor in terms of practical use. Thus in consideration of a case ofusing a personal computer of comparatively low processing speed, a realtime process, wherein, while moving the control point Q9, shown in FIG.20, reciprocatingly to the left and right, a new gamma curve Cb isdetermined by computation each time and displaying a new image usingthis new gamma curve Cb, is poor in terms of practical use.

Thus in carrying out the method described in this Section 10, aplurality of gamma curves within the range of variation are preferablycomputed in advance prior to display of an image to the operator. Forexample, in the case of performing the adjustments (that is adjustmentsusing sample image Ha) of cyclically moving the control points Q7, Q8,and Q9, shown in FIG. 20, all of the necessary gamma curves aredetermined in advance by computation. Specifically, in the case ofvarying the tone value of the control point Q9 by just±5 for the gammacurve Cb, a total of ten curves, that is, the curve for the case wherethe control point is moved by 5 tone value increments to the left, thecurve for the case where the control point is moved by 4 tone valueincrements to the left, . . . the curve for the case where the controlpoint is moved by 4 tone value increments to the right, and the curvefor the case where the control point is moved by 5 tone value incrementsto the right are computed in advance. The same is applied to the gammacurves Cr and Cb. While the operator performs the adjustment operationsconcerning sample image Ha, the priorly computed plurality of gammacurves are used to perform image display.

Subsequently, based on the three gamma curves Cr, Cg, and Cb obtained asa result of the adjustment operations concerning sample images Ha, aplurality of gamma curves that are obtained by moving the respectivecontrol points Q4, Q5, and Q6 within the prescribed range are determinedbefore the operator performs the adjustment operations concerning thenext sample image Hb. Likewise, based on the three gamma curves Cr, Cg,and Cb obtained as a result of the adjustment operations concerningsample images Hb, a plurality of gamma curves that are obtained bymoving the respective control points Q1, Q2, and Q3 within theprescribed range are determined before the operator performs theadjustment operations concerning the last sample image Hc.

By employing such a method of determining the necessary gamma curves inadvance prior to the image display, smooth image display can performedin comparison to the case where image display is performed whileperforming computations in real time.

INDUSTRIAL APPLICABILITY

The reproduction characteristics measuring device for color monitoraccording to the present invention can be used in applications ofvisually measuring the tone reproduction characteristics of a colormonitor having the function of displaying color images using the threeprimary colors of R, G, and B. In particular, this invention is suitablefor applications of determining highly precise tone reproductioncharacteristics and performing corrections of higher precision in acolor monitor that is used for DTP processes of preparing printed matterand also enables measurements of adequate precision for liquid crystalcolor displays as well as CRT color monitors that have undergone ageddeterioration.

1. A device for measuring tone reproduction characteristics, whichindicate a relationship between input signal tone values and actualdisplay luminance of a color monitor (100) having a function ofdisplaying color images using three primary colors of R, G, and B, thetone reproduction characteristics measuring device for color monitorcomprising: tone value designating means (210), designating acombination of tone values of the three primary colors, R, G, and B, fordisplaying an even pattern of uniform brightness and color in a firstattribute region (50); reference pattern generating means (220)generating a reference pattern in which first sub-regions (61) andsecond sub-regions (62) are mixed at a prescribed area ratio inside asecond attribute region (60), wherein each of the three primary colors,R, G, and B take on a minimum tone value in said first sub-regions andeach of the three primary colors, R, G, and B take on a maximum tonevalue in said second sub-regions; pattern display means (230) defining atest pattern which is arranged from said first attribute region and saidsecond attribute region being positioned so as to contact each other ona screen of the color monitor, and providing prescribed signals to thecolor monitor so that an even pattern, based on the combination of tonevalues designated by said tone value designating means, is displayed insaid first attribute region, and said reference pattern, generated bysaid reference pattern generating means, is displayed in said secondattribute region; tone value varying means (240) varying respective tonevalues designated by said tone value designating means so as to vary abrightness and a color of the even pattern; coincidence signal inputmeans (250) inputting, while a varying operation by said tone valuevarying means is being performed, a coincidence signal indicating arecognition that said first attribute region and said second attributeregion are matched in both brightness and color, from an operator whoviews said test pattern displayed on the screen of the color monitor;and characteristics computing means (260) recognizing a combination oftone values designated by said tone value designating means at a pointwhen said coincidence signal is input, as corresponding tone values ofthe respective primary colors that correspond to a prescribed referenceluminance in accordance with said prescribed area ratio, anddetermining, by computation, tone reproduction characteristics of therespective primary colors based on said reference luminance and saidcorresponding tone values that correspond to each other.
 2. The tonereproduction characteristics measuring device for color monitoraccording to claim 1, wherein: the tone value varying means (240) has afunction of performing two types of varying operations of a brightnessvarying operation, with which the tone values are varied so that mainlya brightness of the even pattern changes, and a color varying operation,with which a tone value is varied so that mainly a color of the evenpattern changes.
 3. The tone reproduction characteristics measuringdevice for color monitor according to claim 2, wherein: the brightnessvarying operation is performed by a task of increasing or decreasing allof respective tone values of the three primary colors, R, G, and B by acommon variation amount, and the color varying operation is performed bya task of increasing or decreasing a tone value of a single specificcolor among the three primary colors, R, G, and B.
 4. The tonereproduction characteristics measuring device for color monitoraccording to claim 1, wherein: the tone value varying means (240)performs variations of the tone values based on operation inputs by theoperator.
 5. The tone reproduction characteristics measuring device forcolor monitor according to claim 4, wherein: the tone value varyingmeans (240) uses a first button (31) that provides an instruction ofmaking the even pattern brighter, a second button (32) that provides aninstruction of making the even pattern darker, a third button (33) thatprovides an instruction of strengthening a component of a specific colorof the even pattern, and a fourth button (34) that provides aninstruction of weakening a component of the specific color of the evenpattern, and performs a varying operation of adding a common variationamount to all of the respective tone values of the three primary colors,R, G, and B, when there is an operation input in regard to the firstbutton, performs a varying operation of subtracting a common variationamount from all of the respective tone values of the three primarycolors, R, G, and B, when there is an operation input in regard to thesecond button, performs a varying operation of adding a prescribedvariation amount to a tone value of the specific color when there is anoperation input in regard to the third button, and performs a varyingoperation of subtracting a prescribed variation amount from a tone valueof the specific color when there is an operation input in regard to thefourth button.
 6. The tone reproduction characteristics measuring devicefor color monitor according to claim 5, wherein: a two-dimensional XYcoordinate system is defined and the respective buttons are positionedso that the first button (31) and the second button (32) are positionedat opposing positions along an X-axis that sandwich an origin and thethird button (33) and the fourth button (34) are positioned at opposingposition along a Y-axis that sandwich the origin.
 7. The tonereproduction characteristics measuring device for color monitoraccording to claim 1, wherein: the tone value varying means (240) variesthe tone values with time in accordance with prescribed rules that havebeen established in advance.
 8. The tone reproduction characteristicsmeasuring device for color monitor according to claim 7, wherein: thetone value varying means (240) has a function of performing two varyingoperations of a brightness varying operation, wherein, by adding orsubtracting a common variation amount at a prescribed timing to or fromall of respective tone values of the three primary colors, R, G, and B,the tone values are varied so that mainly the brightness of the evenpattern changes, and a color varying operation, wherein, by adding orsubtracting a prescribed variation amount at a prescribed timing to orfrom a tone value of one specific color among the three primary colors,R, G, and B, the tone value is varied so that mainly the color of theeven pattern changes, and the coincidence signal input means (250) has abrightness coincidence signal input means, for inputting, while the tonevalue varying means is performing the brightness varying operation, abrightness coincidence signal that indicates a recognition that thebrightness is matched from the operator, and a color coincidence signalinput means, for inputting, while the tone value varying means isperforming the color varying operation, a color coincidence signal thatindicates a recognition that the color is matched from the operator, anddeems that a coincidence signal indicating a recognition of matching ofboth brightness and color is input when both inputs of the brightnesscoincidence signal and the color coincidence signal are completed. 9.The tone reproduction characteristics measuring device for color monitoraccording to claim 8, wherein: when a tone value obtained by a varyingoperation of adding a variation amount exceeds a maximum tone value, acirculation process of incrementing a minimum tone value by an excessamount is performed, and when a tone value obtained by a varyingoperation of subtracting a variation amount falls below the minimum tonevalue, a circulation process of decrementing a maximum tone value by anexcess amount is performed.
 10. The tone reproduction characteristicsmeasuring device for color monitor according to claim 8, wherein: thetone value varying means (240) has a function of starting the colorvarying operation at a point when the brightness coincidence signal isinput while the brightness varying operation is performed, starting thebrightness varying operation at a point when the color coincidencesignal is input while the color varying operation is performed, andrepeatedly executing the brightness varying operation and the colorvarying operation in alternation and has a function of performing arepeated execution while gradually decreasing the tone value variationamount, and the coincidence signal input means (250) deems that thecoincidence signal indicating a recognition of matching of bothbrightness and color is input when both inputs of the brightnesscoincidence signal and the color coincidence signal are completed afterthe variation amount has reached a predefined value.
 11. The tonereproduction characteristics measuring device for color monitoraccording to claim 3, wherein: of the three primary colors, R, G, and B,the primary color B is deemed to be the specific color and tonereproduction characteristics for the primary color B and tonereproduction characteristics in common to the primary colors R and G aredetermined.
 12. The tone reproduction characteristics measuring devicefor color monitor according to claim 1, wherein: the reference patterngenerating means (220) has a function of setting a plurality N of arearatios of the first sub-regions to the second sub-regions and generatingN reference patterns that differ mutually in reference luminance, andthe characteristics computing means (260) has a function of determiningthe tone reproduction characteristics for the respective primary colorsbased on N corresponding tone values obtained for N test patterns usingthe N reference patterns.
 13. The tone reproduction characteristicsmeasuring device for color monitor according to claim 12, wherein: thecharacteristics computing means (260) defines a two-dimensionalcoordinate system in which a first coordinate axis is set for tone valueand a second coordinate axis is set for luminance, plots N points havingrespective luminance values and corresponding tone values as coordinatevalues on the coordinate system, plots a point having a minimumluminance value and a minimum tone value as coordinate values, and apoint having a maximum luminance value and a maximum tone value ascoordinate values, and determines a curve passing through the total of(N+2) plotted points in a form of a graph that indicates the tonereproduction characteristics.
 14. The tone reproduction characteristicsmeasuring device for color monitor according to claim 13, wherein: N isset equal to 3, a total of five points are plotted, and upon referringto these five points as a first point to a fifth point in the order ofincreasing coordinate value along the first coordinate axis, a firstfunction curve, passing through the first, second, and third points andtaking a form of expressing the luminance as a power of the tone value,and a second function curve, passing through the third, fourth, andfifth points and taking a form of expressing the luminance as a power ofthe tone value are determined by computation, and a curve formed byjoining the first function curve and the second function curve is deemedto be the curve expressing the tone reproduction characteristics. 15.The tone reproduction characteristics measuring device for color monitoraccording claim 1, wherein: the reference pattern generating means (220)forms the first sub-regions and the second sub-regions from unit cellshaving the same shape and size and forms the reference pattern from atwo-dimensional array of these unit cells.
 16. The tone reproductioncharacteristics measuring device for color monitor according to claim15, wherein: the reference pattern is formed by arraying rectangularunit cells in a two-dimensional array, and for arbitrary odd numbers iand j, a cell group, formed of four unit cells of a unit cell of an i-throw and a j-th column, a unit cell of the i-th row and a (j+1)-thcolumn, a unit cell of an (i+1)-th row and the j-th column, and a unitcell of the (i+1)-th row and the (j+1)-th column, is defined, and acommon positioning pattern of the first sub-regions and the secondsub-regions is applied for all cell groups.
 17. The tone reproductioncharacteristics measuring device for color monitor according to claim16, wherein: among the four unit cells which make up a cell group, firstsub-regions are formed by a pair of unit cells adjacent diagonally andsecond sub-regions are formed by a remaining pair of unit cells so as toconstitute a reference pattern with an area ratio of 1:1.
 18. The tonereproduction characteristics measuring device for color monitoraccording to claim 16, wherein: among the four unit cells which make upa cell group, one unit cell constitutes one sub-region and remainingthree unit cells constitute the other sub-region so as to constitute areference pattern with an area ratio of 3:1 or 1:3.
 19. The tonereproduction characteristics measuring device for color monitoraccording to claim 1, wherein: a contour of the first attribute regionor the second attribute region that makes up the test pattern is made ofa circle or an ellipse.
 20. The tone reproduction characteristicsmeasuring device for color monitor according to claim 1, wherein: oneattribute region that makes up the test pattern is made of a pluralityof regions positioned in a dispersed manner and the other attributeregion is made of a background portion thereof.
 21. The tonereproduction characteristics measuring device for color monitoraccording to claim 20, wherein: a total area of the first attributeregion is made equal to a total area of the second attribute region. 22.The tone reproduction characteristics measuring device for color monitoraccording to claim 20, wherein: a plurality of regions of the sameattribute that are the same in shape and size are positioned dispersedlyin a two-dimensional plane at a prescribed pitch so that a prescribedspatial frequency is obtained.
 23. The tone reproduction characteristicsmeasuring device for color monitor according to claim 22, wherein: aplurality of one-dimensional region arrays, in each of which a pluralityof regions of the same attribute are positioned in a horizontaldirection at a prescribed pitch Px, are positioned in a verticaldirection at a prescribed pitch Py (where Py=(√{square root over ()}3)/2·Px) and positioned so that among mutually adjacentone-dimensional region arrays, the phase is shifted by half a pitch. 24.The tone reproduction characteristics measuring device for color monitoraccording to claim 22, wherein: regions of the same attribute arepositioned dispersedly at a prescribed pitch by which a spatialfrequency that exhibits good sensitivity in regard to both brightnessdifference discrimination characteristics and color differencediscrimination characteristics for the operator viewing the test patternis obtained.
 25. The tone reproduction characteristics measuring devicefor color monitor according to claim 22, wherein: a first pitch, bywhich a spatial frequency that exhibits good sensitivity in regard tobrightness difference discrimination characteristics for the operatorviewing the test pattern is obtained, and a second pitch, by which aspatial frequency that exhibits good sensitivity in regard to colordifference discrimination characteristics for the operator viewing thetest pattern is obtained, are set, and the pattern display means (230)has a function of displaying a test pattern, formed by dispersedlypositioning regions of the same attribute at the first pitch, when abrightness matching recognition task is performed by the operator, anddisplaying a test pattern, formed by dispersedly positioning regions ofthe same attribute at the second pitch, when a color matchingrecognition task is performed by the operator.
 26. (canceled)
 27. Adevice for measuring tone reproduction characteristics, which indicate arelationship between input signal tone values and actual displayluminance of a color monitor (100) having a function of displaying colorimages using three primary colors of R, G, and B, the tone reproductioncharacteristics measuring device for color monitor comprising: tonereproduction characteristics storage means (410) storing provisionaltone reproduction characteristics; image data storage means (420)storing image data of a sample image to be used in measurement; imagedisplay means (430) which assumes that the tone reproductioncharacteristics of the color monitor are to be the provisional tonereproduction characteristics stored in the tone reproductioncharacteristics storage means, performs prescribed tone corrections onimage data stored in the image data storage means so that the sampleimage will be displayed with correct tone reproduction on the colormonitor, and provides corrected image data to the color monitor; aphysical output medium (520) obtained by outputting the sample image ona physical medium based on the image data stored in the image datastorage means; characteristics modifying means (440) receivinginstruction inputs, for making a sample image (510) displayed on ascreen (500) of the color monitor, and a sample image (530) displayed onthe physical output medium (520), close in brightness and color, from anoperator who visually compares the two images; coincidence signal inputmeans (450) inputting a coincidence signal, indicating a recognitionthat both of the images are matched both in brightness and color, fromthe operator; and characteristics output means (460) outputting theprovisional tone reproduction characteristics, stored in the tonereproduction characteristics storage means when the coincidence signalis input, as a formal tone reproduction characteristics of the colormonitor.
 28. The tone reproduction characteristics measuring device forcolor monitor according to claim 27, wherein: image data of a pluralityM of sample images that differ in overall brightness are stored in theimage data storage means (420) and M physical output media (520),respectively corresponding to the M sample images, are prepared; and thecharacteristics modifying means (440), upon receiving an instructioninput concerning an i-th sample image among the M sample images,performs modifications stressed on “a portion corresponding to abrightness of the i-th sample image” on the provisional tonereproduction characteristics stored in the tone reproductioncharacteristics storage means.
 29. The tone reproduction characteristicsmeasuring device for color monitor according to claim 28, wherein: thetone reproduction characteristics storage means (410) stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and thecharacteristics modifying means (440), upon receiving an instructioninput concerning an i-th sample image, recognizes a point on a curve,having a representative tone value of the i-th sample image, as acontrol point, and after moving the control point in a prescribeddirection in accordance with the instruction input, modifies the curvesmoothly so that it passes through the control point after movement. 30.The tone reproduction characteristics measuring device for color monitoraccording to claim 29, wherein: a mode value or an average value ofpixel values of all colors of individual pixels indicated by the imagedata stored in the image data storage means is used as a representativetone value of the sample image.
 31. The tone reproductioncharacteristics measuring device for color monitor according to claim28, wherein: the tone reproduction characteristics storage means (410)stores curves, respectively indicating relationships between tone valueand luminance for the three primary colors, R, G, and B, in a form ofgraphs indicating the tone reproduction characteristics, and thecharacteristics modifying means (440), upon receiving an instructioninput concerning an i-th sample image, recognizes a point on a curve,having a representative luminance value of the i-th sample image, as acontrol point, and after moving the control point in a prescribeddirection in accordance with the instruction input, modifies the curvesmoothly so that it passes through the control point after movement. 32.The tone reproduction characteristics measuring device for color monitoraccording to claim 31, wherein: a mode value or an average value ofpixel values of all colors of individual pixels indicated by the imagedata stored in the image data storage means is determined as therepresentative tone value of the sample image, and a value converted bya prescribed conversion method based on the determined representativetone value is used as the representative luminance value of the sampleimage.
 33. The tone reproduction characteristics measuring device forcolor monitor according to claim 31, wherein: an actually measured valueof luminance of an entire sample image on the physical output medium isused as the representative luminance value of the sample image.
 34. Thetone reproduction characteristics measuring device for color monitoraccording to claim 27, wherein: the characteristics modifying means(440) performs processes of varying the tone reproductioncharacteristics with time in accordance with prescribed rules that havebeen established in advance and performs modifications whereinprovisional tone reproduction characteristics when an instruction inputfrom the operator is provided are deemed to be new provisional tonereproduction characteristics.
 35. The tone reproduction characteristicsmeasuring device for color monitor according to claim 34, wherein: imagedata of a plurality M of sample images that differ in overall brightnessare stored in the image data storage means (420) and M physical outputmedia (520), respectively corresponding to the M sample images areprepared, and the characteristics modifying means (440) has a functionof executing processes of performing variations stressed on “a portioncorresponding to a brightness of an i-th sample image among the M sampleimages” on the provisional tone reproduction characteristics stored inthe tone reproduction characteristics storage means (410) for each ofi=1 to M.
 36. The tone reproduction characteristics measuring device forcolor monitor according to claim 35, wherein: the tone reproductioncharacteristics storage means (410) stores curves, respectivelyindicating relationships between tone value and luminance for the threeprimary colors, R, G, and B, in a form of graphs indicating the tonereproduction characteristics, and the characteristics modifying means(440), in executing a process of performing variations stressed on “aportion corresponding to a brightness of an i-th sample image,”recognizes a point on each of the curves, having a representative tonevalue of the i-th sample image, as a control point, moves the controlpoint in prescribed directions cyclically, and modifies the curvesmoothly so that it passes through the control point after movement. 37.The tone reproduction characteristics measuring device for color monitoraccording to claim 36, wherein: a mode value or an average value ofpixel values of all colors of individual pixels indicated by the imagedata stored in the image data storage means is used as therepresentative tone value of the sample image.
 38. The tone reproductioncharacteristics measuring device for color monitor according to claim35, wherein: the tone reproduction characteristics storage means (410)stores curves, respectively indicating relationships between tone valueand luminance for the three primary colors, R, G, and B, in a form ofgraphs indicating the tone reproduction characteristics, and thecharacteristics modifying means (440), in executing a process ofperforming variations stressed on “a portion corresponding to abrightness of an i-th sample image,” recognizes a point on each of thecurves, having a representative luminance value of the i-th sampleimage, as a control point, moves the control point in prescribeddirections cyclically, and modifies the curve smoothly so that it passesthrough the control point after movement.
 39. The tone reproductioncharacteristics measuring device for color monitor according to claim38, wherein: a mode value or an average value of pixel values of allcolors of individual pixels indicated by the image data stored in theimage data storage means is determined as the representative tone valueof the sample image, and a value converted by a prescribed conversionmethod based on the determined representative tone value is used as therepresentative luminance value of the sample image.
 40. The tonereproduction characteristics measuring device for color monitoraccording to claim 38, wherein: an actually measured value of luminanceof an entire sample image on the physical output medium is used as therepresentative luminance value of the sample image.
 41. The tonereproduction characteristics measuring device for color monitoraccording to claim 27, wherein: the characteristics modifying means(440) has a function of performing two types of modifying operations ofa brightness modifying operation of modifying the tone reproductioncharacteristics based on an instruction input for mainly changing thebrightness of the sample image displayed on a screen of the colormonitor, and a color modifying operation of modifying the tonereproduction characteristics based on an instruction input for mainlychanging the color.
 42. The tone reproduction characteristics measuringdevice for color monitor according to claim 41, wherein: the tonereproduction characteristics storage means (410) stores curves,respectively indicating relationships between tone value and luminancefor the three primary colors, R, G, and B, in a form of graphsindicating the tone reproduction characteristics, and thecharacteristics modifying means (440), performs modification on all ofthe respective curves of the three primary colors R, G, and B inperforming the brightness modifying operation, and performs modificationon only a curve of a color to be modified in performing the colormodifying operation.
 43. The tone reproduction characteristics measuringdevice for color monitor according to claim 27, wherein: an image, whichcan be recognized as a substantially achromatic image when viewed by theoperator, is used as the sample image.
 44. (canceled)
 45. A device formeasuring tone reproduction characteristics, which indicate arelationship between input signal tone values and actual displayluminance of a color monitor having a function of displaying colorimages using three primary colors of R, G, and B, the tone reproductioncharacteristics measuring device for color monitor comprising: means fordetermining a correspondence between luminance and tone value by visualrecognition; means for determining a combination of tone values of thethree primary colors that appears to be achromatic; and characteristicscomputing means determining, by computation, the tone reproductioncharacteristics for the respective primary colors from thecorrespondence between luminance and tone value and a combination of thethree primary colors.
 46. The tone reproduction characteristicsmeasuring device for color monitor according to claim 5 wherein: of thethree primary colors, R, G, and B, the primary color B is deemed to bethe specific color and tone reproduction characteristics for the primarycolor B and tone reproduction characteristics in common to the primarycolors R and G are determined.
 47. The tone reproduction characteristicsmeasuring device for color monitor according to claim 8 wherein: of thethree primary colors, R, G, and B, the primary color B is deemed to bethe specific color and tone reproduction characteristics for the primarycolor B and tone reproduction characteristics in common to the primarycolors R and G are determined.